AM-CSIC and MIC-OAN groups
[1] A Three-dimensional View of the Remnant of Nova Persei 1901 (GK Per) — Liimets, T.; Corradi, R. L. M.; Santander-García, M.; Villaver, E.; Rodríguez-Gil, P.; Verro, K.; Kolka, I.
The Astrophysical Journal — DOI: 10.1088/0004-637X/761/1/34
Journal Impact Factor (2011): 6.024
We present a kinematical study of the optical ejecta of GK Per. It is based on proper-motion measurements of 282 knots from ~20 images spanning 25 years. Doppler shifts are also computed for 217 knots. The combination of proper motions and radial velocities allows a unique three-dimensional view of the ejecta to be obtained. These results raise some problems with the previous interpretations of the evolution of GK Per. In particular, the idea of a strong interaction of the outflow with the surrounding medium in the southwest quadrant is not supported by our data.
[2] The hyperfine structure in the rotational spectrum of CF+ — Guzmán, V.; Roueff, E.; Gauss, J.; Pety, J.; Gratier, P.; Goicoechea, J. R.; Gerin, M.; Teyssier, D.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201220174
Journal Impact Factor (2011): 4.587
CF+ has recently been detected in the Horsehead and Orion Bar photo-dissociation regions. The J = 1-0 line in the Horsehead is double-peaked in contrast to other millimeter lines. The origin of this double-peak profile may be kinematic or spectroscopic. We compute the fluorine spin rotation constant of CF+ using high-level quantum chemical methods and determine the relative positions and intensities of each hyperfine component. This information is used to fit the theoretical hyperfine components to the observed CF+ line profiles, thereby employing the hyperfine fitting method in GILDAS. The fluorine spin rotation constant of CF+ is 229.2 kHz. This way, the double-peaked CF+ line profiles are well fitted by the hyperfine components predicted by the calculations. The unusually large hyperfine splitting of the CF+ line therefore explains the shape of the lines detected in the Horsehead nebula, without invoking intricate kinematics in the UV-illuminated gas.
[3] The complete far-infrared and submillimeter spectrum of the Class 0 protostar Serpens SMM1 obtained with Herschel. Characterizing UV-irradiated shocks heating and chemistry — Goicoechea, J. R.; Cernicharo, J.; Karska, A.; Herczeg, G. J.; Polehampton, E. T.; Wampfler, S. F.; Kristensen, L. E.; van Dishoeck, E. F.; Etxaluze, M.; Berné, O.; Visser, R.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201219912
Journal Impact Factor (2011): 4.587
We present the first complete ∼55−671 μm spectral scan of a low-mass Class 0 protostar (Serpens SMM1) taken with the PACS and SPIRE spectrometers onboard Herschel. More than 145 lines have been detected, most of them rotationally excited lines of 12CO (full ladder from Ju = 4−3 to 42−41 and Eu/k = 4971 K), H2O (up to 818−707 and Eu/k = 1036 K), OH (up to 2Π1/2 J = 7/2−5/2 and Eu/k = 618 K), 13CO (up to Ju = 16−15), HCN and HCO+ (up to Ju = 12−11). Bright [Oi]63, 145 μm and weaker [C ii]158 and [C i]370, 609 μm lines are also detected, but excited lines from chemically related species (NH3, CH+, CO+, OH+ or H2O+) are not. Dissociative J-shocks produced by a jet impacting the ambient material are the most probable origin of [Oi] and OH emission and of a significant fraction of the warm CO emission. In addition, H2O photodissociation in UV-irradiated non-dissociative shocks along the outflow cavity walls can also contribute to the [Oi] and OH emission.
[4] Rotational spectrum of formamide up to 1 THz and first ISM detection of its ν12 vibrational state — Motiyenko, R. A.; Tercero, B.; Cernicharo, J.; Margulès, L.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201220033
Journal Impact Factor (2011): 4.587
We measured the rotational spectrum of formamide in the frequency range 400-950 GHz. The ground and first excited vibrational state of the normal species as well as the ground state of 13C isotopic species were analysed. The results obtained represent an extension by a factor of two in frequency range compared to previous studies. Of all transition frequencies in the dataset about 45% are new measurements. A reliable set of rotational constants allows accurate predictions of transition frequencies in the THz domain. Based on the spectroscopic results, the ν12 = 1 excited vibrational state of formamide was detected in the IRAM 30 m line survey of Orion KL for the first time in the Interstellar Medium.
[5] 3D-PDR: a new three-dimensional astrochemistry code for treating photodissociation regions — Bisbas, T. G.; Bell, T. A.; Viti, S.; Yates, J.; Barlow, M. J.
Monthly Notices of the Royal Astronomical Society — DOI: 10.1111/j.1365-2966.2012.22077.x
Journal Impact Factor (2011): 4.9
Various numerical codes treating one-dimensional PDRs have been developed in the past, simulating the complexity of chemical reactions occurring and providing a better understanding of the structure of a PDR. In this paper we present the three-dimensional code, 3D-PDR, which can treat PDRs of arbitrary density distribution. The code solves the chemistry and the thermal balance self-consistently within a given three-dimensional cloud. It calculates the total heating and cooling functions at any point in a given PDR by adopting an escape probability method. We find that the code is able to reproduce the benchmarking results of various other one-dimensional numerical codes treating PDRs. We also find that the accurate treatment of the radiation field in the fully three-dimensional treatment of PDRs can in some cases leads to different results when compared to a standard one-dimensional treatment
[6] Chemical tracers of high-metallicity environments — Bayet, E.; Davies, T. A.; Bell, T. A.; Viti, S.
Monthly Notices of the Royal Astronomical Society — DOI: 10.1111/j.1365-2966.2012.21330.x
Journal Impact Factor (2011): 4.9
We present for the first time a detailed study of the properties of molecular gas in metal-rich environments such as early-type galaxies (ETGs). We have explored photon-dominated region chemistry for a wide range of physical conditions likely to be appropriate for these sources. We derive fractional abundances of the 20 most chemically reactive species as a function of the metallicity, as a function of the optical depth and for various volume number gas densities, far-ultraviolet (FUV) radiation fields and cosmic ray ionization rates. Discussion of favourable line ratios to be used for the estimation of supersolar metallicities and α-elements are also provided.
[7] The IRAM-30 m line survey of the Horsehead PDR. II. First detection of the l-C3H+ hydrocarbon cation — Pety, J.; Gratier, P.; Guzmán, V.; Roueff, E.; Gerin, M.; Goicoechea, J. R.; Bardeau, S.; Sievers, A.; Le Petit, F.; Le Bourlot, J.; and 2 coauthors
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201220062
Journal Impact Factor (2011): 4.587
Pure gas-phase chemistry models do not succeed in reproducing the measured abundances of small hydrocarbons in the interstellar medium. Information on key gas-phase progenitors of these molecules sheds light on this problem. We aim to constrain the chemical content of the Horsehead mane with a millimeter unbiased line survey at two positions, namely the photo-dissociation region (PDR) and the nearby shielded core. This project revealed a consistent set of eight unidentified lines toward the PDR position. We associate them to the l-C3H+ hydrocarbon cation, which enables us to constrain the chemistry of small hydrocarbons. Six out of the eight unidentified lines observable in the millimeter bands are detected with a signal-to-noise ratio from 6 to 19 toward the Horsehead PDR, while the two last ones are tentatively detected. This is the first detection of the l-C3H+ hydrocarbon in the interstellar medium. Laboratory spectroscopy is underway to confirm these results. Interferometric imaging is needed to firmly constrain the small hydrocarbon chemistry in the Horsehead.
[8] OPACOS: OVRO Post-AGB CO (1-0) Emission Survey. I. Data and Derived Nebular Parameters — Sánchez Contreras, C.; Sahai, R.
The Astrophysical Journal Supplement Series — DOI:10.1088/0067-0049/203/1/16
Journal Impact Factor (2011): 13.456
We have performed interferometric observations of the 12CO (J = 1–0) emission in a sample of 27 objects spanning different evolutionary stages from the late asymptotic giant branch (late-AGB), through the post-AGB (pAGB) phase, and to the planetary nebula (PN) stage, but dominated by pAGB objects and young PNs (≥ 81%). In this paper (the first in a series) we present our maps and main nebular properties derived for the whole sample. We report first detections of 12CO (J = 1–0) emission in 13 targets and confirm emission from several previous marginal detections. The molecular envelope probed by 12CO (J = 1–0) emission is extended for 18 (out of 24) sources; envelope asymmetries and/or velocity gradients are found in most extended objects.
[9] Discovery of the methoxy radical, CH3O toward B1: Dust grain and gas-phase chemistry in cold dark clouds — Cernicharo, J.; Marcelino, N.; Roueff, E.; Gerin, M.; Jiménez-Escobar, A.; Muñoz-Caro, G. M.
The Astrophysical Journal Letters — DOI:10.1088/2041-8205/759/2/L43
Journal Impact Factor (2011): 5.526
We report on the discovery of the methoxy radical (CH3O) toward the cold and dense core B1-b based on the observation, with the IRAM 30 m radio telescope, of several lines at 3 and 2 mm wavelengths. Besides this new molecular species we also report on the detection of many lines arising from methyl mercaptan (CH3SH), formic acid (HCOOH), propynal (HCCCHO), acetaldehyde (CH3CHO), dimethyl ether H3OCH3), methyl formate (CH3OCOH), and the formyl radical (HCO). Nevertheless, laboratory experiments indicate that the CH3O isomer released to the gas phase is CH2OH rather than the methoxy one. Possible gas-phase formation routes to CH3O from OH and methanol are discussed.
[10] Influence of collisional rate coefficients on water wapour excitation — Daniel, F.; Goicoechea, J. R.; Cernicharo, J.; Dubernet, M.-L.; Fauré, A.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201219749; 11/2012
Journal Impact Factor (2011): 4.587
Water is a key molecule in many astrophysical studies that deal with star or planet forming regions, evolved stars, and galaxies. Its high dipole moment makes this molecule subthermally populated under the typical conditions of most astrophysical objects. This motivated calculation of various sets of collisional rate coefficients (CRC) for H2O (with He or H2), which are needed to model its rotational excitation and line emission. This work aims to underline the impact that the new available set of CRC have on interpretations of water vapour observations.
[11] IRAS 19520+2759: a 105 Lsolar massive young stellar object driving a collimated outflow — Palau, A.; Sánchez Contreras, C.; Sahai, R.; Sánchez-Monge, Á.; Rizzo, J. R.
Monthly Notices of the Royal Astronomical Society — DOI: 10.1093/mnras/sts131
Journal Impact Factor (2011): 4.9
In this paper, we present interferometric 12CO (1–0), 13CO (1–0), C18O (1–0) and 2.6mm continuum images of the infrared source IRAS 19520+2759 together with complementary single-dish observations of CS (1–0), obtained with the 34 m antenna DSS-54 at the Madrid Deep Space Communications Complex, as well as archive images at different wavelengths. We propose that IRAS 19520+2759 could be an example of the recent theoretical prediction of ‘bloated’ or ‘swollen’ star, i.e. a massive young stellar object whose radius has increased due to effects of accretion at a high-mass accretion rate.
[12] Chemical Analysis of a Diffuse Cloud along a Line of Sight toward W51: Molecular Fraction and Cosmic-Ray Ionization Rate — Indriolo, N.; Neufeld, D. A.; Gerin, M.; Geballe, T. R.; Black, J. H.; Menten, K. M.; Goicoechea, J. R.
The Astrophysical Journal — DOI: 10.1088/0004-637X/758/2/83
Journal Impact Factor (2011): 6.024
Absorption lines from the molecules OH+,H2O+, and H3+ have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. This is an important step in the future use of OH+ and H2O+ on their own as tracers of the cosmic-ray ionization rate.
[13]Chemistry of C3 and carbon chain molecules in DR21(OH) — Mookerjea, B.; Hassel, G. E.; Gerin, M.; Giesen, T.; Stutzki, J.; Herbst, E.; Black, J. H.; Goldsmith, P. F.; Menten, K. M.; Krełowski, J.; De Luca, M.; Csengeri, T.; Joblin, C.; Kaźmierczak, M.; Schmidt, M.; Goicoechea, J. R.; Cernicharo, J.
Astronomy & Astrophysics — DOI:10.1051/0004-6361/201219287
Journal Impact Factor (2011): 4.587
We aim to identify the primary C3 formation routes in dense star-forming regions following a chemical network producing species like CCH and c-C3H2 in the star-forming cores associated with DR21(OH), a high-mass star-forming region. We interpret the observed lower C3 abundance in MM1 as compared to MM2 and the envelope to be due to the destruction of C3 in the more evolved MM1. The timescale for the chemistry derived for the envelope is consistent with the dynamical timescale of 2 Myr derived for DR21(OH) in other studies.
[14] The CHESS Survey of the L1157-B1 Shock Region: CO Spectral Signatures of Jet-driven Bow Shocks — Lefloch, B.; Cabrit, S.; Busquet, G.; Codella, C.; Ceccarelli, C.; Cernicharo, J.; Pardo, J. R.; Benedettini, M.; Lis, D. C.; Nisini, B.
The Astrophysical Journal Letters — DOI:10.1088/2041-8205/757/2/L25
Journal Impact Factor (2011): 5.526
The unprecedented sensitivity of Herschel coupled with the high resolution of the HIFI spectrometer permits studies of the intensity–velocity relationship I(v) in molecular outflows, over a higher excitation range than possible up to now. Over the course of the CHESS Key Program, we have observed toward the bright bow shock region L1157-B1, the CO rotational transitions between J = 5–4 and J = 16–15 with HIFI, and the J = 1–0, 2–1, and 3–2 with the IRAM 30 m and the Caltech Submillimeter Observatory telescopes. We find that the CO J = 2–1 intensity–velocity relation observed in various other molecular outflows is satisfactorily fit by similar exponential laws, which may hold an important clue to their entrainment process.
[15] Modeling the physical and excitation conditions of the molecular envelope of NGC 7027 — Santander-García, M.; Bujarrabal, V.; Alcolea, J.
Astronomy & Astrophysics — DOI:10.1051/0004-6361/201219211
Journal Impact Factor (2011): 4.587
The Heterodyne Instrument for the Far Infrared (HIFI) aboard Herschel is an invaluable tool because it opens a new window (most of the sub-mm and far-infrared range is only accessible from space) from which to probe warm molecular gas (∼50–1000 K). This paper presents a radiative transfer, spatio-kinematic modeling of the molecular envelope of the young planetary nebula NGC 7027 in several high- and low-J 12CO and 13CO transitions observed by Herschel/HIFI and the IRAM 30-m radio telescope, and discusses the structure and dynamics of the molecular envelope. The striking presence of H2O in NGC 7027, a C-rich nebula, is likely due to photo-induced chemistry from the hot central star, although formation of water by shocks cannot be ruled out. The computed molecular mass of the nebula is 1.3 Msolar, compatible with that derived from previous works.
[16] Two short mass-loss events that unveil the binary heart of Minkowski’s Butterfly Nebula — Castro-Carrizo, A.; Neri, R.; Bujarrabal, V.; Chesneau, O.; Cox, P.; Bachiller, R.
Astronomy & Astrophysics — DOI:10.1051/0004-6361/201118726
Journal Impact Factor (2011): 4.587
We investigate the extended equatorial distribution around the early bipolar planetary nebula M 2−9 (“Minkowski’s Butterfly Nebula”) to gather new information on the mechanism of the axial ejections. Here we present subarcsecond angular-resolution observations of the 12CO J = 2−1 line and continuum emission with the Plateau de Bure interferometer. The data reveal two ring-shaped and eccentric structures at the equatorial basis of the two coaxial optical lobes. The presence of a stellar system with a modest-mass companion at the center of such an elongated bipolar PN strongly supports the binary-based models, because these are more easily able to explain the frequent axisymmetric ejections in PNe.
[17] Herschel/HIFI observations of CO, H2O and NH3 in Monoceros R2 — Pilleri, P.; Fuente, A.; Cernicharo, J.; Ossenkopf, V.; Berné, O.; Gerin, M.; Pety, J.; Goicoechea, J. R.; Rizzo, J. R.; Montillaud, J.; González-García, M.; Joblin, C.; Le Bourlot, J.; Le Petit, F.; Kramer, C.
Astronomy & Astrophysics — DOI:10.1051/0004-6361/201118481
Journal Impact Factor (2011): 4.587
We present new observations ([CII], 12CO, 13CO, C18O, o-H2O, p-H2O, o-H218O and o-NH3) obtained with the HIFI instrument onboard Herschel and the IRAM-30m telescope.We investigated the physical conditions in which these lines arise by analyzing their velocity structure and spatial variations. Using a large velocity gradient approach, we modeled the line intensities and derived an average abundance of H2O and NH3 across the region. The Meudon PDR code, which includes only gas-phase chemical networks, can account for the measured water abundance in the high velocity gas as long as we assume that it originates from a ≤ 1 mag hot expanding layer of the PDR, i.e. that the outflow has only a minor contribution to this emission. To explain the water and ammonia abundances in the rest of the cloud, the molecular freeze out and grain surface chemistry would need to be included.
[18] The Chemistry of Interstellar OH+, H2O+, and H3O+: Inferring the Cosmic-Ray Ionization Rates from Observations of Molecular Ions — Hollenbach, D.; Kaufman, M. J.; Neufeld, D.; Wolfire, M.; Goicoechea, J. R.
The Astrophysical Journal — DOI: 10.1088/0004-637X/754/2/105
Journal Impact Factor (2011): 6.024
We model the production of OH+, H2O+, and H3O+ in interstellar clouds, using a steady-state photodissociation region code that treats the freezeout of gas species, grain surface chemistry, and desorption of ices from grains. The code includes polycyclic aromatic hydrocarbons (PAHs), which have important effects on the chemistry.
[19] Spectroscopic parameters for silacyclopropynylidene, SiC2, from extensive astronomical observations toward CW Leo (IRC +10216) with the Herschel satellite — Müller, H. S. P.; Cernicharo, J.; Agúndez, M.; Decin, L.; Encrenaz, P.; Pearson, J. C.; Teyssier, D.; Waters, L. B. F. M.
Journal of Molecular Spectroscopy — DOI: http://dx.doi.org/10.1016/j.jms.2012.07.003; 08/2012
Journal Impact Factor (2011): 1.512
A molecular line survey has been carried out toward the carbon-rich asymptotic giant branch star CW Leo employing the HIFI instrument on board of the Herschel satellite. Numerous features from 480 GHz to beyond 1100 GHz could be assigned unambiguously to the fairly floppy SiC2 molecule. However, predictions from laboratory data exhibited large deviations from the observed frequencies even after some lower frequency data from this survey were incorporated into a fit. Therefore, we present a combined fit of all available laboratory data together with data from radio-astronomical observations.
[20] Molecular abundances in the inner layers of IRC +10216 — Agúndez, M.; Fonfría, J. P.; Cernicharo, J.; Kahane, C.; Daniel, F.; Guélin, M.
Astronomy & Astrophysics — DOI:10.1051/0004-6361/201218963
Journal Impact Factor (2011): 4.587
Observations towards IRC +10216 of CS, SiO, SiS, NaCl, KCl, AlCl, AlF, and NaCN have been carried out with the IRAM 30-m telescope in the 80-357.5 GHz frequency range. We aim at studying the abundances, throughout the whole circumstellar envelope of the carbon star IRC +10216, of several molecules formed in the inner layers in order to constrain the different processes at work in such regions. We find that in the inner layers CS, SiO, and SiS have abundances relative to H2 of 4 × 10-6, 1.8 × 10-7, and 3 × 10-6, respectively, and that CS and SiS have significant lower abundances in the outer envelope, which implies that they actively contribute to the formation of dust. Moreover, in the inner layers, the amount of sulfur and silicon in gas phase molecules is only 27% for S and 5.6% for Si, implying that these elements have already condensed onto grains, most likely in the form of MgS and SiC.
[21] Warm HCN in the Planet Formation Zone of GV Tau N — Fuente, A.; Cernicharo, J.; Agúndez, M.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/754/1/L6
Journal Impact Factor (2011): 5.526
The Plateau de Bure Interferometer has been used to map the continuum emission at 3.4 mm and 1.1 mm together with the J = 1→0 and J = 3→2 lines of HCN and HCO+ toward the binary star GV Tau. We detected the HCN 3→2 line only toward the individual disk of GV Tau N, and the emission of the HCO+ 3→2 line toward GV Tau S. Simple calculations indicate that the 3→2 line of HCN is formed in the inner R 300. The high HCN abundance measured in GV Tau N is well explained by photochemical processes in the warm (>400 K) and dense (n > 107 cm–3) disk surface.
[22] Spectral line survey of the ultracompact HII region Monoceros R2 — Ginard, D.; González-García, M.; Fuente, A.; Cernicharo, J.; Alonso-Albi, T.; Pilleri, P.; Gerin, M.; García-Burillo, S.; Ossenkopf, V.; Rizzo, J. R.; Kramer, C.; Goicoechea, J. R.; Pety, J.; Berné, O.; Joblin, C.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201118347
Journal Impact Factor (2011): 4.587
We carried out a 3mm and 1mm spectral survey using the IRAM 30-m telescope towards three positions that represent different physical environments in the ultracompact HII region Mon R2. We detected more than thirty different species. We detected SO+ and C4H suggesting that UV radiation plays an important role in the molecular chemistry of this region. We also detected complex molecules that are not usually found in PDRs (CH3CN, H2CO, HC3N, CH3OH and CH3C2H). Sulfur compounds CS, HCS+, C2S, H2CS, SO and SO2 and the deuterated species DCN and C2D were also identified. Our results show that the high UV/dense PDRs present a different chemistry from that of the low UV case.
[23] Nitrogen hydrides in interstellar gas. II. Analysis of Herschel/HIFI observations towards W49N and G10.6 – 0.4 (W31C) — Persson, C. M.; De Luca, M.; Mookerjea, B.; Olofsson, A. O. H.; Black, J. H.; Gerin, M.; Herbst, E.; Bell, T. A.; Coutens, A.; Godard, B.; Goicoechea, J. R.; Hassel, G. E.; Hily-Blant, P.; Menten, K. M.; Müller, H. S. P.; Pearson, J. C.; Yu, S.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201118686
Journal Impact Factor (2011): 4.587
As a part of the Herschel key programme PRISMAS, we have used the Herschel/HIFI instrument to observe interstellar nitrogen hydrides along the sight-lines towards eight high-mass star-forming regions in order to elucidate the production pathways leading to nitrogen-bearing species in diffuse gas. The upper limits on the NH+ abundance indicate column densities 2–14% of N(NH), which is in contrast to the behaviour of the abundances of CH+ and OH+ relative to the values determined for the corresponding neutrals CH and OH. Surprisingly low values of the ammonia ortho-to-para ratio are found in both sources, ≈0.5–0.7 ± 0.1, in the strongest absorption components. This result cannot be explained by current models as we had expected to find a value of unity or higher.
[24] The IRAM-30m line survey of the Horsehead PDR. I. CF+ as a tracer of C+ and as a measure of the fluorine abundance — Guzmán, V.; Pety, J.; Gratier, P.; Goicoechea, J. R.; Gerin, M.; Roueff, E.; Teyssier, D.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201219449; 07/2012
Journal Impact Factor (2011): 4.587
C+ is a key species in the interstellar medium, but its 158 μm fine structure line cannot be observed from ground-based telescopes. Current models of fluorine chemistry predict that CF+ is the second-most important fluorine reservoir in regions where C+ is abundant. Indeed, CF+ and C+ are the only species observed to date in the Horsehead with a double-peaked line profile caused by kinematics. We therefore propose that CF+, which is detectable from the ground, can be used as a proxy of the C+ layers.
[25] Evaporating very small grains as tracers of the UV radiation field in photo-dissociation regions — Pilleri, P.; Montillaud, J.; Berné, O.; Joblin, C.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201015915; 06/2012
Journal Impact Factor (2011): 4.587
In photo-dissociation regions (PDRs), polycyclic aromatic hydrocarbons (PAHs) may be produced by evaporation of very small grains (VSGs) by the impinging UV radiation field from a nearby star. We quantitatively investigate the transition zone between evaporating VSGs (eVSGs) and PAHs in several PDRs. The fitting tool PAHTAT (PAH Toulouse Astronomical Templates), available to the community as an IDL routine, an be used to trace the intensity of the local UV radiation field in regions where eVSGs evaporate, which correspond to relatively dense (nH = [100,105] cm-3) and UV irradiated PDRs (G0 = [100,5 × 104] ) where H2 emits in rotational lines.
[26] Herschel/HIFI Discovery of HCl+ in the Interstellar Medium — De Luca, M.; Gupta, H.; Neufeld, D.; Gerin, M.; Teyssier, D.; Drouin, B. J.; Pearson, J. C.; Lis, D. C.; Monje, R.; Phillips, T. G.; Goicoechea, J. R.; Godard, B.; Falgarone, E.; Coutens, A.; Bell, T. A.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/751/2/L37; 06/2012
Journal Impact Factor (2011): 5.526
The radical ion HCl+, a key intermediate in the chlorine chemistry of the interstellar gas, has been identified for the first time in the interstellar medium with the Herschel Space Observatory’s Heterodyne Instrument for the Far-Infrared. The models reproduce well the interstellar absorption, and the frequencies inferred from the astronomical observations are in exact agreement with those calculated using spectroscopic constants derived from the laboratory data. These observations also yield the unexpected result that HCl+ accounts for 3%-5% of the gas-phase chlorine toward W49N and W31C, values several times larger than the maximum fraction (~1%) predicted by chemical models.
[27] Soft X-Ray Irradiation of H2S Ice and the Presence of S2 in Comets — Jiménez-Escobar, A.; Muñoz Caro, G. M.; Ciaravella, A.; Cecchi-Pestellini, C.; Candia, R.; Micela, G.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/751/2/L40; 06/2012
Journal Impact Factor (2011): 5.526
Little is known about the effects of X-rays in interstellar ices. To understand the sulfur depletion in dense clouds and the presence of S2 in comets, we simulated experimentally the soft X-ray processing (0.3 keV) of H2S ice for the first time. Experiments were performed under ultrahigh vacuum conditions at 8 K using infrared and quadrupole mass spectrometry to monitor the solid and gas phases, respectively. A UV irradiation experiment using a similar dose was made for comparison. Based on our experimental results, we propose that S2 in comets could be formed by dissociation of H2S2 in the ice.
[28] Herschel/HIFI observation of highly excited rotational lines of HNC toward IRC +10 216 — Daniel, F.; Agúndez, M.; Cernicharo, J.; De Beck, E.; Lombaert, R.; Decin, L.; Kahane, C.; Guélin, M.; Müller, H. S. P.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201118449
Journal Impact Factor (2011): 4.587
We report the detection in emission of various highly excited rotational transitions of HNC (J = 6–5 through J = 12–11) toward the carbon-star envelope IRC +10 216 using the HIFI instrument on-board the Herschel Space Observatory. Observations of the J = 1–0 and J = 3–2 lines of HNC with the IRAM 30-m telescope are also presented. The lines observed with HIFI have upper level energies corresponding to temperatures between 90 and 340 degrees Kelvin, and trace a warm and smaller circumstellar region than that seen in the interferometric maps of the J = 1–0 transition. The presence of HNC in the circumstellar envelope of IRC +10 216 is consistent with formation from the precursor ion HCNH+, which in turn is produced through several proton transfer reactions which are triggered by cosmic-ray ionization.
[29] The wideband backend at the MDSCC in Robledo. A new facility for radio astronomy at Q- and K-bands — Rizzo, J. R.; Pedreira, A.; Gutiérrez Bustos, M.; Sotuela, I.; Larrañaga, J. R.; Ojalvo, L.; Franco, M.; Cernicharo, J.; García-Miró, C.; Castro Cerón, J. M.; Kuiper, T. B. H.; Vázquez, M.; Calvo, J.; Baquero, A.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201218833; 06/2012
Journal Impact Factor (2011): 4.587
We have developed and built a new wideband backend for the Robledo antennas, with the objectives (1) to optimize the available time and enhance the efficiency of radio astronomy in MDSCC; and (2) to tackle new scientific cases that were impossible to investigate with the existing autocorrelator. The new wideband backend fulfills the requirements and makes better use of the available time for radio astronomy, which opens new possibilities to potential users. The first setup provides 1.5 GHz of instantaneous bandwidth in a single polarization, using 8192 channels and a frequency resolution of 212 kHz; upgrades under way include a second FFTS card, and two high-resolution cores providing 100 MHz and 500 MHz of bandwidth, and 16 384 channels. These upgrades will permit simultaneous observations of the two polarizations with instantaneous bandwidths from 100 MHz to 3 GHz, and spectral resolutions from 7 to 212 kHz.
[30] The fight for accretion: discovery of intermittent mass transfer in BB Doradus in the low state — Rodríguez-Gil, P.; Schmidtobreick, L.; Long, K. S.; Gänsicke, B. T.; Torres, M. A. P.; Rubio-Díez, M. M.; Santander-García, M.
Monthly Notices of the Royal Astronomical Society — DOI: 10.1111/j.1365-2966.2012.20783.x; 05/2012
Journal Impact Factor (2011): 4.900
Our long-term photometric monitoring of southern nova-like cataclysmic variables with the 1.3-m Small and Moderate Aperture Research Telescope System (SMARTS) telescope found BB Doradus fading from V˜ 14.3 towards a deep low state at V˜ 19.3 in 2008 April. Here we present time-resolved optical spectroscopy of BB Dor in this faint state in 2009. The optical spectrum in quiescence is a composite of a hot white dwarf with Teff= 30 000 ± 5000 K and a M3-M4 secondary star with narrow emission lines (mainly of the Balmer series and He I) superposed. Two scenarios are proposed to explain the extra emission: impact of the material on the outer edge of a cold, remnant accretion disc, or the combined action of a moderately magnetic white dwarf (B1≲ 5 MG) and the magnetic activity of the donor star.
[31] Comparative study of CH+ and SH+ absorption lines observed towards distant star-forming regions — Godard, B.; Falgarone, E.; Gerin, M.; Lis, D. C.; De Luca, M.; Black, J. H.; Goicoechea, J. R.; Cernicharo, J.; Neufeld, D. A.; Menten, K. M.; Emprechtinger, M.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201117664; 04/2012
Journal Impact Factor (2011): 4.587
The HIFI instrument onboard Herschel has allowed high spectral resolution and sensitive observations of ground-state transitions of three molecular ions: the methylidyne cation CH+, its isotopologue 13CH+, and sulfanylium SH+. Because of their unique chemical properties, a comparative analysis of these cations provides essential clues to the link between the chemistry and dynamics of the diffuse interstellar medium. The CH+, 13CH+, and SH+ line profiles are therefore statistically broader than those of most species detected in absorption in diffuse interstellar gas (e.g. HCO+, CH, or CN). The observed dynamical and chemical properties of SH+ and CH+ are proposed to trace the ubiquitous process of turbulent dissipation, in shocks or shears, in the diffuse ISM and the specific environment of the Galactic centre regions.
[32] The abundance of C18O and HDO in the envelope and hot core of the intermediate mass protostar NGC 7129 FIRS 2 — Fuente, A.; Caselli, P.; McCoey, C.; Cernicharo, J.; Johnstone, D.; Fich, M.; van Kempen, T.; van Dishoeck, E.; Yıldız, U.; Visser, R.; Kristensen, L.; Alonso-Albi, T.; Herpin, F.; Tisi, S.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201118478 Journal
Impact Factor (2011): 4.587
This paper is dedicated to the modeling of the C18O and HDO lines in NGC 7129 FIRS 2. Our goal is to investigate the chemistry in the envelope and hot core of this young intermediate-mass protostar. Herschel data combined with ground based observations have allowed us to estimate the C18O and HDO abundance in the protostellar envelope and hot core of an IM protostar. The HDO abundance in the hot core is ~0.4-1 × 10-7, similar to that found in the hot corinos NGC 1333 IRAS 2A and IRAS 16293-2422. The C18O abundance, at ≈ 1.6 × 10-8, is a factor of 10 lower than the reference value.
[33] Star-formation laws in luminous infrared galaxies. New observational constraints on models — García-Burillo, S.; Usero, A.; Alonso-Herrero, A.; Graciá-Carpio, J.; Pereira-Santaella, M.; Colina, L.; Planesas, P.; Arribas, S.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201117838; 03/2012
Journal Impact Factor (2011): 4.587
We aim to expand the sample of extreme starbursts, represented by local luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs), with high-quality observations in the 1-0 line of HCN, which is taken as a proxy for the dense molecular gas content. The new data presented in this work allow us to enlarge in particular the number of LIRGs studied in HCN by a factor 3 compared to previous works. We have used the IRAM 30 m telescope to observe a sample of 19 LIRGs in the 1-0 lines of CO, HCN and HCO+. The analysis of the new data proves that the efficiency of star formation in the dense molecular gas (SFEdense) of extreme starbursts is a factor 3-4 higher compared to normal galaxies. We find a duality in KS laws that is further reinforced if we account for the likely different conversion factor for HCN (αHCN) in extreme starbursts and for the unobscured star-formation rate in normal galaxies. This result extends the more extreme bimodal behavior of star-formation laws that was derived from CO molecular lines by two recent surveys to the higher molecular densities probed by HCN lines.
[34] Microwave and submillimeter spectroscopy and first ISM detection of 18O-methyl formate — Tercero, B.; Margulès, L.; Carvajal, M.; Motiyenko, R. A.; Huet, T. R.; Alekseev, E. A.; Kleiner, I.; Guillemin, J. C.; Møllendal, H.; Cernicharo, J.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201117072; 02/2012
Journal Impact Factor (2011): 4.587
We present an experimental study and a theoretical analysis of two 18O-methyl formate isotopologues, which were subsequently detected for the first time in Orion KL. The experimental spectra of both methyl formate isotopologues recorded in the microwave and sub-mm range from 1 to 660 GHz. Both spectra were analysed by using the rho-axis method (RAM) which takes into account the CH3 internal rotation. We obtained spectroscopic constants of both 18O- methyl formate with high accuracy. Thousands of transitions were assigned and others predicted, which allowed us to detect both species in the IRAM 30 m line survey of Orion KL.
[35] The Illumination and Growth of CRL 2688: An Analysis of New and Archival Hubble Space Telescope Observations — Balick, B.; Gomez, T.; Vinković, D.; Alcolea, J.; Corradi, R. L. M.; Frank, A.
The Astrophysical Journal — DOI: 10.1088/0004-637X/745/2/188; 02/2012
Journal Impact Factor (2011): 6.024
We present four-color images of CRL2688 obtained in 2009 using the Wide-Field Camera 3 on HST. The F606W image is compared with archival images in very similar lters to monitor the proper motions of nebular structure. We fi nd that the bright N{S lobes have expanded uniformly by 2.5% and that the ensemble of rings has translated radially by 0:0007 in 6.65 y. We constructed a two-dimensional dust scattering model of stellar radiation through CRL 2688 that successfully reproduces the details of the nebular geometry, its integrated spectral energy distribution, and nearly all of its color variations. The model implies that the optical opacity of the lobes >~ 1, the dust particle density in the rings decreases as radius-3, and that the mass and momentum of the AGB winds and their rings have increased over time.
[36] Soft X-Ray Irradiation of Pure Carbon Monoxide Interstellar Ice Analogues — Ciaravella, A.; Jiménez-Escobar, A.; Muñoz Caro, G. M.; Cecchi-Pestellini, C.; Candia, R.; Giarrusso, S.; Barbera, M.; Collura, A.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/746/1/L1; 02/2012
Journal Impact Factor (2011): 5.526
There is an increasing evidence for the existence of large organic molecules in the interstellar and circumstellar medium. Laboratory experiments show that irradiation of interstellar ice analogues by fast particles or ultraviolet radiation can induce significant chemical complexity. We present irradiation of a pure carbon monoxide ice using a soft X-ray spectrum peaked at 0.3 keV. Analysis of irradiated samples shows formation of CO2, C2O, C3O2, C3, C4O, and CO3/C5. To our knowledge this is the first report on X-ray photolysis of CO ices. The present results show that X-ray irradiation represents an efficient photo-chemical way to convert simple ices to more complex species.
[37] Herschel/HIFI observations of molecular emission in protoplanetary nebulae and young planetary nebulae — Bujarrabal, V.; Alcolea, J.; Soria-Ruiz, R.; Planesas, P.; Teyssier, D.; Cernicharo, J.; and 13 co-authors
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201117646; 01/2012
Journal Impact Factor (2011): 4.587
We performed Herschel/HIFI observations of intermediate-excitation molecular lines in the far-infrared/submillimeter range in a sample of ten young planetary nebulae. The high spectral resolution provided by HIFI allows the accurate measurement of the line profiles. We have detected FIR/sub-mm lines of several molecules, in particular of 12CO, 13CO, and H2O. Emission from other species, like NH3, OH, H218O, HCN, SiO, etc., has been also detected. Wide profiles showing sometimes spectacular line wings have been found. We have mainly studied the excitation properties of the high-velocity emission, which is known to come from fast bipolar outflows. We argue that the differences in temperature in the different nebulae can be caused by cooling after the gas acceleration (that is probably caused by shocks); for instance, CRL 618 is a case of very recent acceleration, less than ~100 yr ago, while the fast gas in OH 231.8+4.2 was accelerated ~1000 yr ago.
[38] Herschel/HIFI observations of O-rich AGB stars: molecular inventory — Justtanont, K.; Khouri, T.; Maercker, M.; Alcolea, J.; Decin, L.; Olofsson, H.; Schöier, F. L.; Bujarrabal, V.; Marston, A. P.; Teyssier, D.; Cernicharo, J.; and 9 co-authors
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201117524; 01/2012
Journal Impact Factor (2011): 4.587
We used the HIFI instrument to observe nine O-rich asymptotic giant-branch (AGB) stars, mainly in the H2O and high rotational CO lines. We investigate the correlation between line luminosity, line ratio and mass-loss rate, line width and excitation energy. Maser emission is detected in both the ortho- and para-H2O molecules. The line luminosities of ground state lines of ortho- and para-H2O, the high-J CO and NH3 lines show a clear correlation with mass-loss rate. The line ratios of H2O and NH3 relative to CO J = 6-5 correlate with the mass-loss rate while ratios of higher CO lines to the 6-5 is independent of it. In most cases, the expansion velocity derived from the observed line width of highly excited transitions formed relatively close to the stellar photosphere is lower than that of lower excitation transitions, formed farther out, pointing to an accelerated outflow.
GAPT-IAA group
[39] GRANADA: A Generic RAdiative traNsfer AnD non-LTE population algorithm — Funke, B.; López-Puertas, M.; García-Comas, M.; Kaufmann, M.; Höpfner, M.; Stiller, G. P.
Journal of Quantitative Spectroscopy and Radiative Transfer — DOI: http://dx.doi.org/10.1016/j.jqsrt.2012.05.001; 09/2012
Journal Impact Factor (2011): 3.193
We present in this paper the Generic RAdiative traNsfer AnD non-LTE population Algorithm (GRANADA). This model is able to compute non-LTE populations for vibrational, rotational, spin (i.e., NO and OH), and electronic (i.e., O2) states in a given planetary atmosphere. The model is very flexible and can be used for computing very accurate non-LTE populations or for calculating reasonably accurate but at high speed non-LTE populations in order to implement it into non-LTE remote sensing retrievals. We describe the model in detail and present an update of the non-LTE collisional processes and their rate coefficients for the most important molecules in Earth’s atmosphere. In addition, we have applied the model to the most important atmospheric infrared emitters including 13 species (H2O, CO2, O3, N2O, CO, CH4, O2, NO, NO2, HNO3, OH, N2, and HCN) and 460 excited vibrational or electronic energy levels.
RT-IAC group
[40] Signal detection for spectroscopy and polarimetry — Asensio-Ramos, A; Manso Sainz, R.
Astronomy & Astrophysics DOI — 10.1051/0004-6361/201220124
Journal Impact Factor (2011): 4.587
We present in this paper a Bayesian technique for detecting spectropolarimetric signals. The technique is based on applying the nonparametric relevance vector machine to the observations, which allows us to compute the evidence for the presence of the signal and compute the more probable signal. The method is suited for analyzing data from experimental instruments onboard space missions and rockets aiming at detecting spectropolarimetric signals in unexplored regions of the spectrum, such as the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) sounding rocket experiment.
[41] The Hanle effect of Lyα in a magnetohydrodynamic model of the solar transition region — Stepan, J.; Trujillo Bueno, J.; Carlsson, M.; Leenaarts, J.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/758/2/L43
Journal Impact Factor (2011): 5.526
In order to understand the heating of the solar corona it is crucial to obtain empirical information on the magnetic field in its lower boundary (the transition region). To this end, we need to measure and model the linear polarization produced by scattering processes in strong UV lines, such as the hydrogen Lyα line. Here, we report on the Lyα scattering polarization signals we have calculated in a realistic model of an enhanced network region, resulting from a state-of-the-art radiation magnetohydrodynamic simulation. This model is characterized by spatially complex variations of the physical quantities at transition region heights. The results of our investigation lead us to emphasize that scattering processes in the upper solar chromosphere should indeed produce measurable linear polarization in Lya. More importantly, we show that via the Hanle effect the model’s magnetic field produces significant changes in the emergent Q/I and U/I profiles. Therefore, we argue that by measuring the polarization signals produced by scattering processes and the Hanle effect in Lya and contrasting them with those computed in increasingly realistic atmospheric models, we should be able to decipher the magnetic, thermal, and dynamic structure of the upper chromosphere and transition region of the Sun.
[42] Hanle Effect for Stellar Dipoles and Quadropoles — Manso Sainz, R.; Martínez González, M. J.
The Astrophysical Journal — DOI: 10.1088/0004-637X/760/1/7
Journal Impact Factor (2011): 6.024
We derive exact expressions for the degree of lineal polarization over a resolved or integrated stellar disc due to resonance scattering and the Hanle effect from a dipolar or quadrupolar distribution of magnetic fields. We apply the theory of scattering polarization within the formalism of the spherical tensors representation for the density matrix and radiation field. The distribution of linear polarization over the stellar disk for different configurations of the magnetic field is studied and its topology discussed. For an unresolved dipole, the resulting polarization can be expressed in terms of just three functions (of the inclination angle and effective dipole strength) that are calculated numerically and their behavior discussed. Dipolar and (aligned) quadrupoles are considered in some detail, but the techniques here—in particular, the extensive use of the spherical tensor formalism for polarization—can easily be applied to more general field configurations.
[43] Dead Calm Areas in the Very Quiet Sun — Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz, R.; Hijano, E.
The Astrophysical Journal — DOI: 10.1088/0004-637X/755/2/175
Journal Impact Factor (2011): 6.024
Dead calm areas, characterized by a very low magnetic signal and a lack of organized loop-like structures at the detection level of our instruments, cannot be explained as just statistical fluctuations of a Poisson spatial process. We argue that this is an intrinsic characteristic of the mechanism that generates the magnetic fields in the very quiet Sun. The spatiotemporal coherences and the clumpy structure of the phenomenon suggest a recurrent, intermittent mechanism for the generation of magnetic fields in the quietest areas of the Sun.
[44] Analytical Calculation of Stokes Profiles of Rotating Stellar Magnetic Dipole — Martínez González, M. J.; Asensio Ramos, A.
The Astrophysical Journal — DOI: 10.1088/0004-637X/755/2/96
Journal Impact Factor (2011): 6.024
The observation of the polarization emerging from a rotating star at different phases opens up the possibility to map the magnetic field in the stellar surface thanks to the well-known Zeeman–Doppler imaging. When the magnetic field is sufficiently weak, the circular and linear polarization profiles locally in each point of the star are proportional to the first and second derivatives of the unperturbed intensity profile, respectively. We show that the weak-field approximation (for weak lines in the case of linear polarization) can be generalized to the case of a rotating star including the Doppler effect and taking into account the integration on the stellar surface.
[45] Anomalous Circular Polarization Profiles in the He I 1083.0 nm Multiplet from Solar Spicules — Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz, R.; Beck, C.; Belluzzi, L.
The Astrophysical Journal — DOI: 10.1088/0004-637X/759/1/16
Journal Impact Factor (2011): 6.024
We report Stokes vector observations of solar spicules and a prominence in the He i 1083 nm multiplet carried out with the Tenerife Infrared Polarimeter. The observations show linear polarization profiles that are produced by scattering processes in the presence of a magnetic field. After a careful data reduction, we demonstrate the existence of extremely asymmetric Stokes V profiles in the spicular material that we are able to model with two magnetic components along the line of sight, and under the presence of atomic orientation in the energy levels that give rise to the multiplet. We discuss some possible scenarios that can generate the atomic orientation in spicules. We stress the importance of spectropolarimetric observations across the limb to distinguish such signals from observational artifacts.
[46] Non-local thermodynamic equilibrium inversions from a 3D magnetohydrodynamic chromospheric model — de la Cruz Rodríguez, J.; Socas-Navarro, H.; Carlsson, M.; Leenaarts, J.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201218825; 07/2012
Journal Impact Factor (2011): 4.587
This study aims to establish the diagnostic capabilities of non-local thermodynamical equilibrium (NLTE) inversion techniques of Stokes profiles induced by the Zeeman effect in the Ca ii λ8542 Å line. Our NLTE inversions applied to quiet-Sun synthetic observations provide reasonably good estimates of the chromospheric magnetic field, line-of-sight velocities and somewhat less accurate, but still very useful, estimates of the temperature. Three-dimensional scattering of photons cause cool pockets in the chromosphere to be invisible in the line profile and consequently they are also not recovered by the inversions. To successfully detect Stokes linear polarization in this quiet snapshot, a noise level below 10-3.5 is necessary.
[47] Discovery of Hα satellite emission in a low state of the SW Sextantis star BB Doradus — Schmidtobreick, L.; Rodríguez-Gil, P.; Long, K. S.; Gänsicke, B. T.; Tappert, C.; Torres, M. A. P.
Monthly Notices of the Royal Astronomical Society — DOI: 10.1111/j.1365-2966.2012.20653.x; 05/2012
Journal Impact Factor (2011): 4.900
BB Dor was observed during its low state in 2009. Signatures of both binary components are revealed in the average optical spectrum; no signature of accretion is observed. Narrow emission lines of Hα, He I and Na D, as well as TiO absorption troughs, trace the motion of the irradiated secondary star. We detect two additional components in the Hα emission line that share many characteristics of similar ‘satellite’ lines observed in the low state of magnetic cataclysmic variables of AM Her type. It is the first time such emission components are detected for an SW Sex star.
[48] The Scattering Polarization of the Lyα Lines of H I and He II Taking into Account Partial Frequency Redistribution and J-state Interference Effects — Belluzzi, L.; Trujillo Bueno, J.; Stepán, J.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/755/1/L2
Journal Impact Factor (2011): 5.526
Here we report that the joint action of partial frequency redistribution and J-state interference produces much more complex fractional linear polarization (Q/I) profiles, with large amplitudes in their wings. Such wing polarization signals turn out to be very sensitive to the temperature structure of the atmospheric model, so that they can be exploited for constraining the thermal properties of the solar chromosphere. Finally, we show that the approximation of CRD without J-state interference is however suitable for estimating the amplitude of the linear polarization signals in the core of the lines, where the Hanle effect operates.
[49] The polarization of the solar Mg II h and k lines — Belluzzi, L.; Trujillo Bueno, J.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/750/1/L11
Journal Impact Factor (2011): 5.526
Although the h and k lines of Mg II are expected to be of great interest for probing the upper solar chromosphere, relatively little is known about their polarization properties which encode the information on the magnetic field. Here we report the first results of an investigation whose main goal is to understand the physical mechanisms that control the scattering polarization across these resonance lines and to achieve a realistic radiative transfer modeling in the presence of arbitrary magnetic fields. We show that the joint action of partial frequency redistribution (PRD) and quantum interference between the upper J-levels of the two lines produces a complex fractional linear polarization (Q/I) pattern with large polarization amplitudes in the blue and red wings, and a negative feature in the spectral region between the two lines. Another remarkable peculiarity of the Q/I profile is a conspicuous antisymmetric signal around the center of the h line, which cannot be obtained unless both PRD and J-state interference effects are taken into account. In the core of the k line, PRD effects alone produce a triplet peak structure in the Q/I profile, the modeling of which can also be achieved via the two-level atom approximation. In addition to the Hanle effect in the core of the k line, we also emphasize the diagnostic potential of the circular polarization produced by the Zeeman effect in the h and k lines, as well as in other Mg II lines located in their wings.
[50] Scattering Polarization in the Ca II Infrared Triplet with Velocity Gradients — Carlin, E. S.; Manso Sainz, R.; Asensio Ramos, A.; Trujillo Bueno, J.
The Astrophysical Journal — DOI: 10.1088/0004-637X/751/1/5; 05/2012
Journal Impact Factor (2011): 6.024
In this theoretical investigation, we focus on the effect that gradients in the macroscopic vertical velocity field have on the non-magnetic scattering polarization signals, establishing the basis for general cases. We demonstrate that the solar plasma velocity gradients may have a significant effect on the linear polarization produced by scattering in chromospheric spectral lines. In particular, we show the impact of velocity gradients on the anisotropy of the radiation field and on the ensuing fractional alignment of the Ca II levels.
[51] Model Selection for Spectropolarimetric Inversions — Asensio Ramos, A.; Manso Sainz, R.; Martínez González, M. J.; Viticchié, B.; Orozco Suárez, D.; Socas-Navarro, H.
The Astrophysical Journal — DOI: 10.1088/0004-637X/748/2/83; 04/2012
Journal Impact Factor (2011): 6.024
We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios (S/Ns) favor models without gradients along the line of sight. If the observations show clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large S/Ns favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future.
[52] Influence of phase-diversity image reconstruction techniques on circular polarization asymmetries — Asensio Ramos, A.; Martínez González, M. J.; Khomenko, E.; Martínez Pillet, V.
Astronomy & Astrophysics — DOI: 10.1051/0004-6361/201117729; 03/2012
Journal Impact Factor (2011): 4.587
We analyze the robustness of circular polarization asymmetries to phase-diversity image reconstruction techniques. Although asymmetries are often difficult to define in the quiet Sun due to the complexity of the Stokes V profiles, we show how asymmetries are degraded with spatial and spectral smearing. The results indicate that, although image reconstruction techniques reduce the spatial smearing, they can modify the asymmetries of the profiles, which are mainly caused by the appearance of spatially-correlated noise.
[53] The Lyα Lines of H I and He II: A Differential Hanle Effect for Exploring the Magnetism of the Solar Transition Region — Trujillo Bueno, J.; Stepan, J.; Belluzzi, L.
The Astrophysical Journal Letters — DOI: 10.1088/2041-8205/746/1/L9; 02/2012
Journal Impact Factor (2011): 5.526
The Lyα line of He II at 304 Å is one of the spectral lines of choice for EUV channels of narrowband imagers on board space telescopes, which provide spectacular intensity images of the outer solar atmosphere. Since the magnetic field information is encoded in the polarization of the spectral line radiation, it is important to investigate whether the He II line radiation from the solar disk can be polarized, along with its magnetic sensitivity. Here we report some theoretical predictions concerning the linear polarization signals produced by scattering processes in this strong emission line of the solar transition region, taking into account radiative transfer and the Hanle effect caused by the presence of organized and random magnetic fields. Even the development of a narrowband imaging polarimeter for the He II 304 Å line alone would be already of great diagnostic value for probing the solar transition region.
ABIDIN-CSIC group
[54] Dynamically biased statistical model for the ortho/para conversion in the H2 + H3+ → H3+ + H2 reaction — Gómez-Carrasco, S.; González-Sánchez, L.; Aguado, A.; Sanz-Sanz, C.; Zanchet, A.
The Journal of Chemical Physics — doi: 10.1063/1.4747548
Journal Impact Factor (2011): 3.333
In this work we present a dynamically biased statistical model to describe the evolution of the title reaction from statistical to a more direct mechanism, using quasi-classical trajectories (QCT). The method is based on the one previously proposed by Park and Light [J. Chem. Phys. 126, 044305 (2007)]. A recent global potential energy surface is used here to calculate the capture probabilities, instead of the long-range ion-induced dipole interactions. The dynamical constraints are introduced by considering a scrambling matrix which depends on energy and determine the probability of the identity/hop/exchange mechanisms. These probabilities are calculated using QCT. It is found that the high zero-point energy of the fragments is transferred to the rest of the degrees of freedom, what shortens the lifetime of H5+ complexes and, as a consequence, the exchange mechanism is produced with lower proportion. This matrix allows to obtain a ratio of hop/exchange mechanisms, α(T), in rather good agreement with recent experimental results by Crabtree et al. [J. Chem. Phys. 134, 194311 (2011)] at room temperature. At lower temperatures, however, the present simulations predict too high ratios because the biased scrambling matrix is not statistical enough. This demonstrates the importance of applying quantum methods to simulate this reaction at the low temperatures of astrophysical interest.
[55] Wave packet calculations on nonadiabatic effects for the O(3P)+HF(1Σ+) reaction under hyperthermal conditions — Gómez-Carrasco, S.; Bulut, N.; Bañares, L.; Roncero, O.
The Journal of Chemical Physics — doi: 10.1063/1.4753811
Journal Impact Factor (2011): 3.333
We present wave packet calculations of total and state-to-state reaction probabilities and integral cross sections for the nonadiabatic dynamics of the O(3P)+HF→F(2P)+OH(2Π) reaction at hyperthermal collision energies ranging from 1.2 to 2.4 eV. The validity of the centrifugal sudden approximation is discussed for the title reaction and a comprehensive investigation of the influence of nonadiabatic effects on the dynamics of this reactive system at high (hyperthermal) collision energies is presented. A critical discussion of nonadiabatic effects on the dynamics of the title reaction is carried out by comparing with the reverse reaction and the characteristics of the adiabatic and diabatic potential energy surfaces involved.
[56] An accurate study of the dynamics of the C+OH reaction on the second excited 14A″ potential energy surface — Zanchet, A.; González-Lezana, T.; Roncero, O.; Jorfi, M.; Honvault, P.; Hankel, M.
The Journal of Chemical Physics — doi: http://dx.doi.org/10.1063/1.4705426
Journal Impact Factor (2011): 3.333
The dynamics of the C(3P)+OH(X2Π) → CO(a3Π)+H(2S) on its second excited potential energy surface, 14A, have been investigated in detail by means of an accurate quantum mechanical (QM) time-dependent wave packet (TDWP) approach. Reaction probabilities for values of the total angular momentum J up to 50 are calculated and integral cross sections for a collision energy range which extends up to 0.1 eV are shown. The comparison with quasi-classical trajectory (QCT) and statistical methods reveals the important role played by the double well structure existing in the potential energy surface. The ability to stop individual trajectories selectively at specific locations inside the potential energy surface makes the QCT version of the statistical approach a better option to understand the overall dynamics of the process.
[57] A theoretical study on electronic predissociation in the NeBr2 van der Waals molecule — Hernández-Lamoneda, R.; Sanz-Sanz, C.; Roncero, O.; Pio, J. M.; Taylor, M. A.; Janda, K. C.
Chemical Physics — DOI: 10.1016/j.chemphys.2011.09.015; 05/2012
Journal Impact Factor (2011): 1.896
We present the first comprehensive ab initio study of the Ne–Br2 potential energy surfaces and the non-adiabatic couplings between the valence excited electronic states. These ab initio results are used to obtain 3-D approximate potentials for each electronic state, and these potentials are used in a wave packet calculation of the competing electronic predissociation and vibrational predissociation dynamics. The results of this calculation are in excellent agreement with both experimental results and a previous empirical fit to the experiments. Success in the case presented here is largely due to the fact that the VP dynamics for the vibrational levels in this study are in the simple, direct regime. Understanding the simple case so thoroughly provides new hope that the more complicated examples, such as ArI2 and NeCl2, for which experiment and theory are not currently in accord, may yet yield to analysis.
[58] Simulation of the infrared predissociation spectra of H5+ — Aguado, A.; Sanz-Sanz, C.; Villarreal, P.; Roncero, O.
Physical Review A DOI: 10.1103/PhysRevA.85.032514; 05/2012
Journal Impact Factor (2011): 2.878
A quantum study of the bound states and infrared predissociation spectra of H5+ is done using a recently proposed global and accurate potential-energy surface [ Aguado et al. J. Chem. Phys. 133 024306 (2010)]. The bound states are calculated for seven degrees of freedom using an iterative Lanczos method, yielding a dissociation energy in very good agreement with the available experimental data. The predissociation states are described by a wave-packet treatment considering a shared-proton model, in which the three-dimensional motion of the central atom is described using non-Jacobi bond coordinates. The justification of this model is that the change in the electric dipole moment is larger as a function of the motion of the central atom, responsible for the proton transfer in the H3++H2→H2+H3+ reaction. The electric dipole moment is calculated at the level of coupled-cluster theory with single and double excitations and fitted in nine dimensions to an analytical function. With it, the infrared predissociation spectrum is simulated, yielding a reasonable agreement with recent measurements.
[59] Theoretical simulations of the vibrational predissociation spectra of H5+ and D5+ clusters — Valdés, A.; Barragán, P.; Sanz-Sanz, C.; Prosmiti, R.; Villarreal, P.; Delgado-Barrio, G.
Theoretica Chimica Acta — DOI: 10.1007/s00214-012-1210-2; 04/2012
Journal Impact Factor (2011): 2.162
In the present study, the effect of the potential energy surface representation on the infrared spectra features of the H5+ and D5+ clusters is investigated. For the spectral simulations, we adopted a recently proposed (Sanz-Sanz et al. in Phys Rev A 84:060502-1–4, 2011) two-dimensional adiabatic quantum model to describe the proton-transfer motion between the two H2 or D2 units. The reported calculations make use of a reliable “on the fly” DFT-based potential surface and the corresponding new dipole moment surface. The results of the vibrational predissociation dynamics are compared with earlier and recent experimental data available from mass-selected photodissociation spectroscopy, as well as with previous theoretical calculations based on an analytical ab initio parameterized surfaces. The role of the potential topology on the spectral features is studied, and general trends are discussed.
[60] Communication: Quantum Zeno-based control mechanism for molecular fragmentation — Sanz-Sanz, C.; Sanz, A. S.; González-Lezana, T.; Roncero, O.; Miret-Artés, S.
The Journal of Chemical Physics — doi: 10.1063/1.3698278; 04/2012
Journal Impact Factor (2011): 3.333
A quantum control mechanism is proposed for molecular fragmentation processes within a scenario grounded on the quantum Zeno effect. In particular, we focus on the van der Waals Ne-Br2 complex, which displays two competing dissociation channels via vibrational and electronic predissociation. Accordingly, realistic three-dimensional wave packet simulations are carried out by using ab initio interaction potentials recently obtained to reproduce available experimental data. Two numerical models to simulate the repeated measurements are reported and analyzed. It is found that the otherwise fast vibrational predissociation is slowed down in favor of the slow electronic (double fragmentation) predissociation, which is enhanced by several orders of magnitude. Based on these theoretical predictions, some hints to experimentalists to confirm their validity are also proposed.
[61] Quantum Zeno effect: Quantum shuffling and Markovianity — Sanz, A. S.; Sanz-Sanz, C.; González-Lezana, T.; Roncero, O.; Miret-Artés, S.
Annals of Physics — doi: http://dx.doi.org/10.1016/j.aop.2011.12.012,; 04/2012
Journal Impact Factor (2011): 2.857
The behavior displayed by a quantum system when it is perturbed by a series of von Neumann measurements along time is analyzed. Because of the similarity between this general process with giving a deck of playing cards a shuffle, here it is referred to as quantum shuffling, showing that the quantum Zeno and anti-Zeno effects emerge naturally as two time limits. Within this framework, a connection between the gradual transition from anti-Zeno to Zeno behavior and the appearance of an underlying Markovian dynamics is found. Accordingly, although a priori it might result counterintuitive, the quantum Zeno effect corresponds to a dynamical regime where any trace of knowledge on how the unperturbed system should evolve initially is wiped out (very rapid shuffling).
[62] Physisorption of helium on a TiO2(110) surface: Periodic and finite cluster approaches — de Lara-Castells, M. P.; Aguirre, N. F.; Mitrushchenkov, A. O.
Chemical Physics — DOI: 10.1016/j.chemphys.2011.07.013; 05/2012
Journal Impact Factor (2011): 1.896
As a proto-typical case of physisorption on an extended transition-metal oxide surface, the interaction of a helium atom with a TiO2(110) – (1 × 1) surface is studied here by using finite cluster and periodic approaches and both wave-function-based (post-Hartree-Fock) quantum chemistry methods and density functional theory. Both classical and advanced finite cluster approaches, based on localized Wannier orbitals combined with one-particle embedding potentials, are applied to provide (reference) coupled-cluster and second-order Möller-Plesset interaction energies. It is shown that, once the basis set is specifically tailored to minimize the basis set superposition error, periodic calculations using the Perdew-Burke-Ernzerhof functional yield short and medium-range interaction potentials in very reasonable agreement with those obtained using the correlated wave-function-based methods, while small long-range dispersion corrections are necessary to reproduce the correct asymptotic behavior. This study is aimed at a subsequent simulation of helium mediated deposition on oxide surfaces.
ABIDIN-CSIC group IN COLL. with DINQUIM-UCM group
[63] Accurate Time-Dependent Wave Packet Study of the Li + H2+ Reaction and Its Isotopic Variants — Aslan, E.; Bulut, N.; Castillo, J. F.; Bañares, L.; Roncero, O.; Aoiz, F. J.
The Journal of Chemical Physics — doi: x.doi.org/10.1021/jp21025
Journal Impact Factor (2011): 3.333
The dynamics and kinetics of the Li + H2+ reaction and its isotopic variants (D2+ and T2+) have been studied by using a time-dependent wave packet (TDWP) coupled-channel (CC) method on the ab initio potential energy surface (PES) of Martinazzo et al. [J. Chem. Phys. 2003, 119, 21]. Total initial v = 0, j = 0 state-selected reaction probabilities for the Li + H2+ reaction and its isotopic variants have been calculated from the threshold up to 1 eV for total angular momenta J from 0 to 90. The TDWP-CC results are in overall good agreement with those obtained applying the TDWP Centrifugal-Sudden (CS) approximation, showing that the CS approximation is rather accurate for the title reaction.
LEMQC-UMU group
[64] Using the Screened Coulomb Potential To Illustrate the Variational Method — Zúñiga, J.; Bastida, A.; Requena, A.
Journal of Chemical Education — DOI: 10.1021/ed2003675
Journal Impact Factor (2011): 0,739
The screened Coulomb potential, or Yukawa potential, is used to illustrate the application of the single and linear variational methods. The trial variational functions are expressed in terms of Slater-type functions, for which the integrals needed to carry out the variational calculations are easily evaluated in closed form. The variational energies of the first two states of the screened Coulomb potential are calculated by minimizing them with respect to the exponential parameters included in the Slater functions using elementary minimization algorithms. The project allows students to concentrate on the fundamentals and the performance of the variational method at its increasingly accurate levels of application to realistic systems.
[65] A spectroscopic potential energy surface for FCN — Zúñiga, J.; Picón, J. A. G.; Bastida, A.; Requena, A.
Journal of Quantitative Spectroscopy and Radiative Transfer — DOI: 10.1016/j.jqsrt.2012.01.023; 07/2012
Journal Impact Factor (2011): 3.193
A potential energy surface for the FCN linear molecule is obtained by nonlinear least-squares fit to the pure (l=0) vibrational terms observed spectroscopically. The potential surface is expressed as a Morse-cosine expansion in valence coordinates, and the vibrational energy levels needed to carry out the fit are calculated variationally using a system of optimal generalized internal coordinates expressly determined for such a purpose. The quality of the potential energy surface fitted is checked by computing the vibrational terms Gv and the rotational constants Bv of the FCN molecule and its isotopologs 19F13C14N and 19F12C15N using a normal hyperspherical coordinate system which facilitates the assignments of normal modes quantum numbers to the vibrational energy levels and the subsequent comparison with the observed values. The spectroscopic FCN potential energy surface obtained is shown to reproduce the vibrational terms of the three molecular species well, and above all their rotational constants, thus endorsing the use of the potential to identify and characterize unobserved infrared bands of these species.
[66] Molecular dynamics with quantum transitions study of the vibrational relaxation of the HOD bend fundamental in liquid D2O — Bastida, A.; Zúñiga, J.; Requena, A.; Miguel, B.
The Journal of Chemical Physics — DOI: 10.1063/1.4729251
Journal Impact Factor (2011): 3.333
The molecular dynamics with quantum transitions method is used to study the vibrational relaxation of the HOD bend fundamental in liquid D2O. All of the vibrational bending degrees of freedom of the HOD and D2O molecules are described by quantum mechanics, while the remaining translational and rotational degrees of freedom are described classically. The effect of the coupling between the rotational and vibrational degrees of freedom of the deuterated water molecules is analyzed. It is shown that intermolecular vibrational energy transfer plays an important role in the relaxation process and also that the transfer of energy into the rotational degrees of freedom is favored over the transfer of energy into the translational motions. The thermalization of the system after the relaxation is reached in a shorter time scale than that of the recovery of the hydrogen bond network. The relaxation and equilibration times obtained compare well with experimental and previous theoretical results.
[67] Antioxidant Properties of β-Carotene Isomers and Their Role in Photosystems: Insights from Ab Initio Simulations — Cerezo, J.; Zúñiga, J.; Bastida, A.; Requena, A.; Cerón-Carrasco, J.P.; Eriksson, L.A.
The Journal of Physical Chemistry A — DOI: 10.1021/jp301485k
Journal Impact Factor (2011): 2.946
In this work we investigate the effect of cis isomerizations and conformational changes on the antioxidant activity of β-carotene, one of the most important pigments in nature. The results obtained are used to analyze the conformational distribution of β-carotene in the well-resolved photosystem I (PS-I) of purple cyanobacteria. It is then shown that the isomers present in this photosystem are those having the lowest calculated relative energies and that those with enhanced antioxidant activity are preferentially located in the inner core of the protein complex.
[68] Hybrid Quantum/Classical Simulations of the Vibrational Relaxation of the Amide I Mode of N-Methylacetamide in D2O Solution — Bastida, A.; Soler, M.A.; Zúñiga, J.; Requena, A.; Kalstein, A.; Fernández-Alberti, S.
The Journal of Physical Chemistry B — DOI: 10.1021/jp210727u
Journal Impact Factor (2011): 3.696
Hybrid quantum/classical molecular dynamics (MD) is applied to simulate the vibrational relaxation (VR) of the amide I mode of deuterated N-methylacetamide (NMAD) in aqueous (D2O) solution. A novel version of the vibrational molecular dynamics with quantum transitions (MDQT) treatment is developed in which the amide I mode is treated quantum mechanically while the remaining degrees of freedom are treated classically. The results extracted from the hybrid MDQT simulations show that the quantum treatment of the amide I mode accelerates the whole VR process versus pure classical simulations and gives better agreement with experiments. The relaxation of the amide I mode is found to be essentially an intramolecular vibrational redistribution (IVR) process with little contribution from the solvent, in agreement with previous theoretical and experimental studies.
[69] Impact of DFT functionals on the predicted magnesium–DNA interaction: an ONIOM study — Cerón-Carrasco, J.P.; Requena, A.; Jacquemin, D.
Theoretical Chemistry Accounts — DOI 10.1007/s00214-012-1188-9
Journal Impact Factor (2011): 2.162
We investigate the descriptions of several density functional theory functionals in modeling the interactions between DNA and magnesium, the divalent cation with the largest intracellular concentration. The aqueous environment is simulated through, on the one hand, explicit solvent molecules present in the first hydration shell and, on the other hand, the well-known polarizable continuum model for the effects of solvation beyond this first shell. Calculations with all methods indicate that the Mg2+ cation coordination to DNA promotes a single PT reaction from the guanine to the cytosine base, characterized by a low back-reaction barrier. These methods can be combined with B97-D functional in ONIOM partition for the description of the stacking effects.
[70] Theoretical vibrational terms and rotational constants for the 15N substituted isotopologues of N2O calculated using normal hyperspherical coordinates — Zúñiga, J.; Bastida, A.; Requena, A.
Journal of Quantitative Spectroscopy and Radiative Transfer — DOI: http://dx.doi.org/10.1016/j.jqsrt.2011.09.017; 01/2012
Journal Impact Factor (2011): 3.193
Variational calculations of the vibrational terms Gv and rotational constants Bv of the 14N15N16O, 15N14N16O and 15N15N16O isotopologues of nitrous oxide are carried out using normal hyperspherical coordinates. The Morse-cosine potential energy surface for N2O previously determined by the authors by fitting to a set of experimental vibrational frequencies is employed. The Gv and Bv spectroscopic constants calculated for the 15N substituted isotopologues show an satisfactory agreement with those experimentally observed for a large number of vibrational bands of these isotopologues recently measured. Predicted calculated values of these spectroscopic constants for unobserved vibrational bands of the 15N substituted isotopologues are given in order to be of help in the identification and characterization of such bands, as a complement to the use of global effective Hamiltonians.
IONTRAP-UPO group
[71] Multipodal coordination of a tetracarboxylic crown ether with NH4+: A vibrational spectroscopy and computational study — Hurtado, P.; Gámez, F.; Hamad, S.; Martínez-Haya, B.; Steill, J.D.; Oomens, J.
Journal of Chemical Physics — doi: 10.1063/1.3693518; 04/2012
Journal Impact Factor (2011): 3.333
The elucidation of the structural requirements for molecular recognition by the crown ether (18-crown-6)-2,3,11,12-tetracarboxylic acid (18c6H4) and its cationic complexes constitutes a topic of current fundamental and practical interest in catalysis and analytical sciences. The flexibility of the central ether ring and its four carboxyl side arms poses important challenges to experimental and theoretical approaches. In this study, infrared action vibrational spectroscopy and quantum mechanical computations are employed to characterize the conformational structure of the isolated gas phase complex formed by the 18c6H4 host with NH4+ as guest. The results show that the most stable gas-phase structure is a barrel-like conformation sustained by tetrapodal H-bonding of the ammonia cation with two C=O side groups and with four oxygen atoms of the ether ring in a bifurcated arrangement. Interestingly, a similar structure had been proposed in previous crystallographic studies.
[72] Conformational landscape of a chiral crown ether: a vibrational circular dichroism spectroscopy and computational study — Avilés Moreno, J. R.; Partal Ureña, F.; López González, J. J.; Gámez, F.; Martínez-Haya, B.
Tetrahedron: Asymmetry — DOI: 10.1016/j.tetasy.2012.02.013; 04/2012
Journal Impact Factor (2011): 2.652
Herein we report a study of the most stable conformers of the chiral crown ether (all-S)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18c6H4), which constitutes a key building block for materials in asymmetric catalysis and enantiomeric separation. Infrared and vibrational circular dichroism spectroscopies are employed to characterize the vibrational modes of the 18c6H4 molecule in a low polarity solvent (CDCl3). The investigation covers a broad range of wavenumbers (800–4000 cm−1) and focuses particularly on the O–H, C–H, CO and C–O stretching modes and on the C–O–H bending mode, which yield the most intense IR and VCD signals. The experimental results are combined with a computational conformational survey and structure optimization at the B3LYP/6-311++G(2d,2p) level. The conformational landscape of 18c6H4 is found to be governed by bowl-like structures sustained by various types of H-bonding arrangements of the carboxylic side chains with each other and with the central crown ether ring.
[73] Tweezer-like Complexes of Crown Ethers with Divalent Metals: Probing Cation-Size-Dependent Conformations by Vibrational Spectroscopy in the Gas Phase — Gamez, F.; Hurtado, P.; Hamad, S.; Martinez-Haya, B.; Berden, G.; Oomens, J.
CHEMPLUSCHEM — DOI: 10.1002/cplu.201100044
Journal Impact Factor (2011): N/A
Crown ethers constitute central building blocks for the synthesis of molecular tweezers capable of trapping cationic species. In this study, isolated ternary complexes comprising two [18]crown-6 (18c6) ether molecules and one divalent cation of varying size (Cu2+, Ca2+, Ba2+) are investigated by means of laser vibrational action spectroscopy and computations. In the ternary (18c6)(2)-Cu2+ complex, one of the crown units folds tightly around the cation, while the second crown ether unit binds peripherally. Such asymmetrical binding manifests itself as a bimodal splitting of the vibrational bands measured for the complex. The size of the cation in the Ca2+ and Ba2+ complexes leads to a progressively more symmetrical coordination of the two crown ether molecules with the metal.
GEM-UVA group
[74] The microwave spectrum of neurotransmitter serotonin — Cabezas, C.; Varela, M.; Peña, I.; López, J. C.; Alonso, J. L.
Physical Chemistry Chemical Physics — DOI: 10.1039/c2cp42654d
Journal Impact Factor (2011): 3.57
A laser ablation device in combination with a molecular beam Fourier-transform microwave spectrometer has allowed the observation of the rotational spectrum of serotonin for the first time. Three conformers of the neurotransmitter have been detected and characterized in the 4–10 GHz frequency range. The complicated hyperfine structure arising from the presence of two 14N nuclei has been fully resolved for all conformers and used for their identification. Nuclear quadrupole coupling constants of the nitrogen atom of the side chain have been used to determine the orientation of the amino group probing the existence of N–H pi interactions involving the amino group and the pyrrole unit in the Gauche-Phenyl conformer (GPh) or the phenyl unit in the Gauche-Pyrrole (GPy) ones.
[75] A broadband Fourier-transform microwave spectrometer with laser ablation source: The rotational spectrum of nicotinic acid — Mata, S.; Peña, I.; Cabezas, C.; López, J. C.; Alonso, J. L.
Journal of Molecular Spectroscopy — DOI: http://dx.doi.org/10.1016/j.jms.2012.08.004; 08/2012
Journal Impact Factor (2011): 1.512
A chirped pulse Fourier transform microwave spectrometer (CP-FTMW) has been combined with a laser ablation source to investigate the broadband rotational spectra of solid biomolecules in the 6.0–18 GHz region. This technique has been successfully applied to the conformational study of nicotinic acid for which two conformers have been characterized for the first time in the gas phase. The quadrupole hyperfine structure originated by a 14N nucleus has been completely resolved for both rotamers using a LA-MB-FTMW spectrometer.
[76] The conformational locking of asparagine — Cabezas, C.; Varela, M.; Peña, I.; Mata, S.; López, J. C.; Alonso, J. L.
Chemical Communications — DOI: 10.1039/C2CC32109B; 05/2012
Journal Impact Factor (2011): 6.169
The present study provides reliable experimental information of the proteinogenic amino acid Asn in the gas phase showing that its conformational landscape is dominated by a single conformer. We have traced back the motif of the selective stabilization of only one conformer. The cooperativity effects of the intramolecular network formed by four hydrogen bonds have been shown to be at the origin of the conformational locking observed for Asn. These results clearly demonstrate that the presence of a polar side chain does not always increase the number of conformations but on the contrary imparts some restrictions on the amount of conformers observed for Asn.
GEM-UVA group IN COLL. with IONTRAP-UPO group
[77] Microwave spectroscopy and quantum chemical investigation of nine low energy conformers of the 15-crown-5 ether — Gámez, F.; Martínez-Haya, B.; Blanco, S.; López, J. C.; Alonso, J. L.
Physical Chemistry Chemical Physics — DOI: 10.1039/c2cp41635b
Journal Impact Factor (2011): 3.57
In this work, we present a systematic investigation of the low energy conformational landscape of the benchmark macrocycle 15-crown-5 ether (15c5) under isolated conditions. Molecular beam Fourier transform microwave spectroscopy is employed to measure a broad ensemble of rotational transitions within the range of 4–11 GHz. The recorded spectra allow us to determine the rotational constants of eight individual 15c5 rotamers which are identified among the nine lowest energy conformers predicted by ab initio MP2 computations. The study illustrates well the variety of conformers of prolate and oblate character that the 15c5 molecule displays within a narrow range of energies. Implications for the supramolecular behavior of 15c5 are discussed.
[78] High-resolution rotational spectroscopy of a cyclic ether — Gámez, F.; Martínez-Haya, B.; Blanco, S.; López, J. C.; Alonso, J. L.
Journal of Physical Chemistry Letters — DOI: 10.1021/jz201678w; 02/2012
Journal Impact Factor (2011): 3.166
The conformational landscape of crown ethers has constituted a central topic in the development of host-guest supramolecular chemistry. We report a high-resolution rotational study of a crown ether, 1,4,7,10,13- pentaoxacyclopentadecane (15-crown-5), by means of molecular beam Fourier transform microwave spectroscopy. The considerable size and the broad range of conformations allowed by the flexibility of the cyclic backbone of this ether pose important challenges to spectroscopy approaches. In this investigation, three stable rotamers of the 15-crown-5 ether have been identified and characterized through their rotational constants and centrifugal distortion coefficients. Ab initio quantum calculations at the MP2 level predict these conformers as the most stable ones for the title system and reproduce accurately their distinct structural features. The results pave the ground for an extensive survey of the conformational landscape of the 15-crown-5 and related cyclic ethers in the near term.
GEM-UVA group IN COLL. with AM-CSIC group
[79] LA-MB-FTMW Spectroscopy of AlCCH and AgCCH with a discharge source — Cabezas, C.; Mata, S.; Daly, A. M.; Martín, A.; Alonso, J. L.; Cernicharo, J.
Journal of Molecular Spectroscopy — DOI: http://dx.doi.org/10.1016/j.jms.2012.07.003; 08/2012
Journal Impact Factor (2011): 1.512
Using a combination of laser ablation and jet cooled FT-MW spectroscopy the pure rotational spectrum of AlCCH and AgCCH in the (X1Σ+) electronic ground state has been recorded and assigned in the 6-20 GHz region. A newly constructed ablation-discharge source has been coupled to our LA-MB-FTMW spectrometer and tested as a generator of metal acetylides. Laser ablation of the pure metal has been demonstrated as a very efficient method to create unstable compounds in the gas phase. The high spectral resolution of our instrument provided an accurate set of rotational, quadrupole (only for AlCCH) and centrifugal distortion constants which are reported for the first time.
DINQUIM-UCM group
[80] Elucidation of the O(1D) + HF → F + OH mechanism by means of quasiclassical trajectories — Jambrina, P. G.; Montero, I.; Aoiz, F. J.; Aldegunde, J.; Alvariño, J. M.
Physical Chemistry Chemical Physics — DOI: 10.1039/c2cp42287e
Journal Impact Factor (2011): 3.570
The dynamics and mechanism of the O(1D) + HF → F + OH reaction have been studied through quasi-classical trajectory calculations carried out on the 11A0 Potential Energy Surface (PES) fitted by Gómez-Carrasco et al. [Chem. Phys. Lett., 2007, 435, 188]. The influence of the collision energy and the initial rovibrational state on the reaction has been considered. As a result of this study, we conclude that for v = 0 the reactive collisions take place exclusively through an indirect mechanism that involves a long-lived complex. Interestingly and somewhat unexpectedly for a barrierless reaction, vibrational excitation causes a large enhancement of the reactivity due to the concurrence of a direct abstraction mechanism. Unlike other reactions also taking place on a barrierless PES featuring deep wells, no insertion mechanism is observed in O(1D) + HF reactive collisions.
[81] Dynamics of the reactions of muonium and deuterium atoms with vibrationally excited hydrogen molecules: Tunneling and vibrational adiabaticity — Jambrina, P. G.; García, E.; Herrero, V. J.; Sáez-Rábanos, V.; Aoiz, F. J.
Physical Chemistry Chemical Physics — DOI:10.1039/C2CP42130E
Journal Impact Factor (2011): 3.570
Quantum mechanical (QM) and quasiclassical trajectory (QCT) calculations have been carried out for the exchange reactions of D and Mu (Mu = muonium) with hydrogen molecules in their ground and first vibrational states. In all the cases considered, the QM rate coefficients, k(T), are in very good agreement with the available experimental results. The QM reaction probabilities and total reactive cross sections show that the total energy thresholds for the reactions of Mu with H2 in ν = 0 and ν = 1 are very similar, whereas for the corresponding reaction with D the ν = 0 total energy threshold is about 0.3 eV lower than that for ν = 1. The results just mentioned can be explained by considering the vibrational adiabatic potentials along the minimum energy path. Most interestingly, the expected tunneling effect in the reaction of Mu with hydrogen molecules occurs for H2 (ν = 1) but not for H2 (ν = 0) where zero-point-energy effects clearly dominate.
[82] A state-to-state dynamical study of the Br + H2 reaction: Comparison of quantum and classical trajectory results — Panda, A.N.; Herráez-Aguilar, D.; Jambrina, P.G.; Aldegunde, J.; Althorpe, S.C.; Aoiz, F.J.
Physical Chemistry Chemical Physics — DOI: 10.1039/C2CP41825H
Journal Impact Factor (2011): 3.570
We present a detailed theoretical investigation of the dynamics corresponding to the strongly endothermic Br + H2 (v = 0–1, j = 0) – H + HBr reaction in the 0.85 to 1.9 eV total energy range. State-averaged and state-to-state results obtained through time-independent wave packet (TIWP) and time-independent quantum mechanical (TIQM) calculations and quasiclassical trajectories (QCT) are compared and analyzed. The agreement in the results obtained with both quantum mechanical results is very good overall. However, although QCT calculations reproduce the general features, their agreement with the QM results is sometimes only qualitative. Consideration of state-to-state processes, in contrast, unveils the existence of multiple mechanisms that give rise to a succession of maxima in the differential cross section (DCS). Such mechanisms correlate with different sets of partial waves and display similar collision times when analyzed through the time-dependent DCS.
[83] Rate coefficients from quantum and quasi-classical cumulative reaction probabilities for the S(D-1) + H-2 reaction — Jambrina, P. G.; Lara, M.; Menéndez, M.; Launay, J. M.; Aoiz, F.J.
Journal of Chemical Physics — DOI: 10.1063/1.4761894
Journal Impact Factor (2011): 3.333
Cumulative reaction probabilities (CRPs) at various total angular momenta have been calculated for the barrierless reaction S(D-1) + H-2 -> SH + H at total energies up to 1.2 eV using three different theoretical approaches: time-independent quantum mechanics (QM), quasiclassical trajectories (QCT), and statistical quasiclassical trajectories (SQCT). The results show that the differences between these two PES are relatively minor and mostly related to the different topologies of the well. In addition, the agreement between the three theoretical methodologies is good, even for the highest total angular momenta and energies. In addition, total CRPs and rate coefficients in the range of 20-1000 K have been calculated using the QCT and SQCT methods and have been found somewhat smaller than the experimental total removal rates of S(D-1).
[84] A new potential energy surface for OH(A (2)Sigma(+))-Kr: The van der Waals complex and inelastic scattering — Chadwick, H.; Brouard, M.; Chang, Y. P.; Eyles, C.J.; Perkins, T.; Seamons, S. A.; Klos, J.; Alexander, M. H.; Aoiz, F.J.
Journal of Chemical Physics — DOI: 10.1063/1.4757859
Journal Impact Factor (2011): 3.333
New ab initio studies of the OH(A(2)Sigma(+))-Kr system reveal significantly deeper potential energy wells than previously believed, particularly for the linear configuration in which Kr is bound to the oxygen atom side of OH(A(2)Sigma(+)). In spite of this difference with previous work, bound state calculations based on a new RCCSD(T) potential energy surface yield an energy level structure in reasonable accord with previous studies. However, the new calculations suggest the need for a reassignment of the vibrational levels of the electronically excited complex. The values of the rotational energy transfer cross sections measured experimentally are in good agreement with those derived from the dynamical calculations on the new adiabatic potential energy surface
[85] H + D-2 Reaction Dynamics in the Limit of Low Product Recoil Energy — Aldegunde, J.; Herraez-Aguilar, D.; Jambrina, P. G.; Aoiz, F. J.; Jankunas, J.; Zare, R. N.
Journal of Physical Chemistry Letters — DOI: 10.1021/jz301192f
Journal Impact Factor (2011): 3.166
Both experiment and theory recently showed that the H + D-2(v = 0, j = 0) -> HD(v’ = 4, j’) + D reactions at a collision energy of 1.97 eV display a seemingly anomalous HD product angular distribution that moves in the backward direction as the value of j’ increases and the corresponding energy available for product recoil decreases. This behavior was attributed to the presence of a centrifugal barrier along the reaction path. Here, we show, using fully quantum mechanical calculations, that for low recoil energies, the collision mechanism is nearly independent of the HD internal state and the HD product becomes aligned, with its rotational angular momentum j’ pointing perpendicular to the recoil momentum k’. As the kinetic energy to overcome this barrier becomes limited, the three atoms adopt a nearly collinear configuration in the transition-state region to permit reaction, which strongly polarizes the resulting HD product. These results are expected to be general for any chemical reaction in the low recoil energy limit.
[86] A classical versus quantum mechanics study of the OH + CO → H + CO2 (J = 0) reaction — García, E.; Aoiz, F.J.; Laganá, A.
Theoretical Chemistry Accounts — DOI: 10.1007/s00214-012-1262-3
Journal Impact Factor (2011): 2.162
Quasiclassical trajectory calculations have been performed for the OH ? CO reaction at zero total angular momentum and collision energies up to 0.4 eV. Calculations have been carried out on the same potential energy surface which was used full-dimensional state-to-state quantum dynamical calculation. The resulting quasiclassical total reaction probability as well as the product rotational and vibrational distributions have been analyzed and compared with the outcomes of a pseudo-quantization treatment of the product vibrational energy. These results have also allowed to investigate the effect of the total angular momentum on the translational energy and angular distributions of the products.
[87] Three-vector correlation in statistical reactions: the role of the triatomic parity — Jambrina, P. G.; Aldegunde, J.; De Miranda, M. P.; Sáez-Rábanos, V.; Aoiz, F. J.
Physical Chemistry Chemical Physics — DOI:10.1039/C2CP41049D; 06/2012
Journal Impact Factor (2011): 3.570
This article presents a methodology for the determination of the k–j–k′ three-vector correlation assuming a statistical model for atom–diatom reactions; k and k′ are the reagent-approach and product-recoil directions, respectively, and j is the rotational angular momentum of the reagent diatomic. Although the polarization of reagent angular momentum is in most cases negligible, conservation of the triatomic parity imposes a certain polarization for some combinations involving low reagent and product rotational states. Statistical and quantum-mechanical polarization-dependent differential cross sections were calculated for the barrierless D+ + H2(v = 0,j) → HD(v′ = 0,j′) + H+ reaction. The agreement between the two is in most cases excellent, confirming the statistical character of the reaction at low and moderate collision energies.
[88] New findings regarding the NO angular momentum orientation in Ar–NO(2Π1/2) collisions — Jambrina, P. G.; Klos, J.; Aoiz, F. J.; De Miranda, M. P.
Physical Chemistry Chemical Physics — DOI: 10.1039/c2cp41043e; 06/2012
Journal Impact Factor (2011): 3.570
This article reports a theoretical study of the stereodynamics of Ar + NO(X2Π, v = 0, j = 1/2, Ω = 1/2, ε = ±1) rotationally inelastic collisions. First, quantum scattering data are used to calculate all differential polarisation moments of the reagent and product molecules; this leads to the observation that the orientations of the reagent and product angular momenta are very strongly correlated. Next, canonical collision mechanisms theory [Aldegunde et al., Phys. Chem. Chem. Phys., 2008, 10, 1139] is used to separate and characterise the stereodynamics of the two independent collision mechanisms that contribute to the collision dynamics; this leads to the observation that the average product orientation is determined by the relative contributions of the two canonical mechanisms, which have comparable importance but are associated with starkly contrasting angular momentum orientations. The central fact of the new explanation is the incoherent, interference-free superposition of two independent collision mechanisms. This makes the new explanation radically different from the only one previously suggested, namely that the experimental observations might be due to quantum interference in a single collision mechanism.
[89] Communication: Rate coefficients from quasiclassical trajectory calculations from the reverse reaction: The Mu+H-2 reaction re-visited — Homayoon, Z.; Jambrina, P. G.; Aoiz, F. J.; Bowman, J. M.
Journal of Chemical Physics — DOI: 10.1063/1.4734316
Journal Impact Factor (2011): 3.333
In a previous paper [P. G. Jambrina et al., J. Chem. Phys. 135, 034310 (2011)] various calculations of the rate coefficient for the Mu + H-2 -> MuH + H reaction were presented and compared to experiment. The widely used standard quasiclassical trajectory (QCT) method was shown to overestimate the rate coefficients by several orders of magnitude over the temperature range 200-1000 K. This was attributed to a major failure of that method to describe the correct threshold for the reaction owing to the large difference in zero-point energies (ZPE) of the reactant H-2 and product MuH (similar to 0.32 eV). In this Communication we show that by performing standard QCT calculations for the reverse reaction and then applying detailed balance, the resulting rate coefficient is in very good agreement with the other computational results that respect the ZPE, (as well as with the experiment) but which are more demanding computationally.
[90] Ab Initio studies of the interaction potential for the Xe-NO(X-2 Pi) van der Waals complex: Bound states and fully quantum and quasi-classical scattering — Klos, J.; Aoiz, F. J.; Menendez, M.; Brouard, M.; Chadwick, H.; Eyles, C. J.
Journal of Chemical Physics — DOI: 10.1063/1.4731286
Journal Impact Factor (2011): 3.333
Adiabatic potential energy surfaces for the ground electronic state of the Xe center dot center dot center dot NO(X-2 Pi) van der Waals complex have been calculated using the spin-restricted coupled cluster method with single, double, and non-iterative triple excitations (RCCSD(T)). The new potential energy surfaces were used to calculate bound states of the complex for total angular momentum quantum numbers up to J = 7/2. The ground state energy of Xe center dot center dot center dot NO(X-2 Pi) is D-0 = 117 cm(-1), which matches the experimental value very accurately (within 3.3%). Scattering calculations of integral and differential cross sections have also been performed using fully quantum close coupling calculations and quasi-classical trajectory method at a collision energy of 63 meV. These calculations reveal the important role played by L-type rainbows in the scattering dynamics of the heavier Rg-NO(X) systems.
[91] Seemingly Anomalous Angular Distributions in H+D-2 Reactive Scattering — Jankunas, J.; Zare, R. N.; Bouakline, F.; Althorpe, S. C.; Herraez-Aguilar, D.; Aoiz, F. J.
Science — DOI: 10.1126/science.1221329
Journal Impact Factor (2011): 31.201
When a hydrogen (H) atom approaches a deuterium (D-2) molecule, the minimum-energy path is for the three nuclei to line up. Consequently, nearly collinear collisions cause HD reaction products to be backscattered with low rotational excitation, whereas more glancing collisions yield sideways-scattered HD products with higher rotational excitation. Here we report that measured cross sections for the H + D-2 -> HD(v’ = 4, j’) + D reaction at a collision energy of 1.97 electron volts contradict this behavior. The anomalous angular distributions match closely fully quantum mechanical calculations, and for the most part quasiclassical trajectory calculations. As the energy available in product recoil is reduced, a rotational barrier to reaction cuts off contributions from glancing collisions, causing high-j’ HD products to become backward scattered.
[92] The effect of parity conservation on the spin-orbit conserving and spin-orbit changing differential cross sections for the inelastic scattering of NO(X) by Ar — Eyles, C.J.; Brouard, M.; Chadwick, H.; Aoiz, F.J.; Kłos, J.; Gijsbertsen, A.; Zhang, X.; Stolte, S.
Physical Chemistry Chemical Physics — DOI:10.1039/C2CP23259F; 03/2012
Journal Impact Factor (2011): 3.570
The fully Λ-doublet resolved state-to-state differential cross sections (DCSs) for the collisions of NO(X, 2Π, v = 0, j = 0.5) with Ar have been shown to depend sensitively on the conservation of the total parity of the NO molecular wavefunction. A simple hard shell, four path model has been employed to determine the relative phase shifts of the paths contributing to the scattering amplitude. The model calculations using the Vsum potential, together with the results of a quasi-quantum treatment, provide good qualitative agreement with the experimental spin–orbit conserving (ΔΩ = 0) DCSs, suggesting that the dynamics for all but the lowest Δj transitions are determined largely by the repulsive part of the potential. The collisions leading to spin-orbit changing transitions (ΔΩ = 1) have been also found to be dominated by repulsive forces, even for the lowest Δj values. However, they are less well reproduced by hard shell calculations, because of the crucial participation of the Vdiff potential in determining the outcome of these collisions.
[93] Orientation effects in Cl + H2 inelastic collisions: Characterization of the mechanisms — Aldegunde, J.; Aoiz, F.J.; González-Sánchez, L.; Jambrina, P.G.; De Miranda, M.P.; Sáez-Rábanos, V.
Physical Chemistry Chemical Physics — DOI: 10.1039/C2CP23252A; 02/2012
Journal Impact Factor (2011): 3.570
Based on quantum mechanical scattering (QM) calculations, we have analyzed the polarization of the product hydrogen molecule in Cl + H2 (v = 0, j = 0) inelastic collisions. The spatial arrangements adopted by the rotational angular momentum and internuclear axis of the departing molecule have been characterized and used to prove that two distinct mechanisms, corresponding to different dynamical regimes, are responsible for the inelastic collisions. Such mechanisms, named as low-b and high-b, correlate with well defined ranges of impact parameter values, add in an essentially incoherent way, and can be clearly differentiated through the quantum mechanical polarization moment that measures the orientation of the products rotational angular momentum with respect to the scattering plane. Other directional effects turn out to fail when it comes to distinguishing the mechanisms. Quasiclassical trajectories (QCT) calculations have been used as a supplement to the purely quantum mechanical analysis. By combining QM and QCT results, which are in very good agreement, we have succeeded in obtaining a clear and meaningful picture of how the two types of collisions take place.
[94] Fully Λ-doublet resolved state-to-state differential cross-sections for the inelastic scattering of NO(X) with Ar — Eyles, C. J.; Brouard, M.; Chadwick, H.; Hornung, B.; Nichols, B.; Yang, C.-H.; Kłos, J.; Aoiz, F. J.; Gijsbertsen, A.; Wiskerke, A. E.
Physical Chemistry Chemical Physics — DOI: 10.1039/C2CP23258H; 02/2012
Journal Impact Factor (2011): 3.570
Fully Λ-doublet resolved state-to-state differential cross-sections (DCSs) for the collisions of the open-shell NO(X, 2Π1/2, ν = 0, j = 0.5) molecule with Ar at a collision energy of 530 cm−1 are presented. Both spin–orbit conserving and spin–orbit changing collisions have been studied, and the previously unobserved structures in the fully quantum state-to-state resolved DCSs are shown to depend sensitively on the change in parity of the wavefunction of the NO molecule on collision. In all cases, the experimental data are shown to be in excellent agreement with rigorous quantum mechanical scattering calculations.
DINQUIM-UCM group IN COLL. with ABIDIN-CSIC group
[95] Accurate Time-dependent Wave Packet Study of the H++LiH Reaction at Early Universe Conditions — Aslan, E.; Bulut, N.; Castillo, J. F.; Bañares, L.; Aoiz, F. J.; Roncero, O.
The Astrophysical Journal — DOI: 10.1088/0004-637X/759/1/31
Journal Impact Factor (2011): 6.024
The dynamics and kinetics of the H+ + LiH reaction have been studied using a quantum reactive time-dependent wave packet (TDWP) coupled-channel quantum mechanical method on an ab initio potential energy surface at conditions of the early universe. The total reaction probabilities for the H+ + LiH(v = 0, j = 0) → H+2 + Li process have been calculated from 5 × 10−3 eV up to 1 eV for total angular momenta J from 0 to 110. Using a Langevin model, integral cross sections have been calculated in that range of collision energies and extrapolated for energies below 5×10−3 eV. The calculated rate constants are found to be nearly independent of temperature in the 10–1000 K interval with a value of ≈10−9 cm3 s−1, which is in good agreement with estimates used in evolutionary models of the early universe lithium chemistry.
GFM-CSIC group
[96] Chemistry in low-pressure cold plasmas: ions of astrophysical interest — Carrasco, E.; Jiménez-Redondo, M.; Tanarro, I.; Herrero, V. J.
Plasma Physics and Controlled Fusion — doi: 10.1088/0741-3335/54/12/124019
Journal Impact Factor (2011): 2.731
The ionic chemistry of various hydrogen mixtures (H2/N2, H2/O2, and H2/air) has been studied in low-pressure hollow cathode discharges. The major ions identified in the different discharges (H+3, N2H+, H3O+ and NH+4) have been also found in astronomical observations or predicted in astrochemical models. The relative stability of the protonated ions in the various mixtures has been investigated in detail. In discharges of H2 with small amounts of N2, O2 and air, appreciable amounts of NH3 and H2O were formed at the reactor walls. The preponderance of the protonated ions in these plasmas was found to be largely dictated by the proton affinity of their respective molecular precursors. Even for small amounts of water and ammonia, proton transfer reactions tend to concentrate the positive charge in H3O+ and, especially, in NH+4 ions. These results support the predictions of some astrochemical models indicating that these ions could be dominant in warm astronomical environments where H2O and NH3 molecules evaporate from dust grain mantels.
[97] Time-resolved diagnostics and kinetic modelling of the ignition transient of a H2 + 10% N2 square wave modulated hollow cathode discharge — Carrasco, E.; Herrero, V. J.; Tanarro, I.
Journal of Physics D: Applied Physics — doi:10.1088/0022-3727/45/30/305201; 07/2012
Journal Impact Factor (2011): 2.544
Time-resolved emission spectroscopy and quadrupole mass spectrometry are used for the experimental diagnostics of a low pressure (8 Pa) modulated dc hollow cathode discharge of H2 + 10% N2. The time-dependent experimental results are reasonably accounted for by a zero-order kinetic model developed in our group and checked previously with steady-state measurements (Carrasco et al 2011 Phys. Chem. Chem. Phys. 13 19561), which is now validated under more stringent conditions. In addition to the discharge precursors, which are partly recycled in wall reactions, NH3 is produced in small but appreciable amounts. The slower evolution of NH3, as compared with H2 and N2, is traced back to the multistep surface reaction mechanism responsible for its production. An analysis of the time variation of optical emission measurements shows that excited NH(c 1Π) radicals are essentially formed in the electron-impact dissociation of NH3.
LHM-UCM group
[98]Vibrational excitation of adsorbed molecules by low-energy photon-emitted electrons: A dynamical model — González-Ureña, A.; Telle, H. H.; Tornero, J.
Journal of Molecular Structure — doi:http://dx.doi.org/10.1016/j.molstruc.2012.07.032
Journal Impact Factor (2011): 1.634
A simple, inelastic electron-scattering dynamical model is presented to account for vibrational excitation in molecular adsorbates. The basic two ingredients of the theoretical model are: (i) the conservation of the total angular momentum, and (ii) the requirement of a critical time to allow for the intra-molecular energy re-arrangement of the transient negative-ion complex. Fits of the model to the data allowed for deducing the energy threshold of the vibrational excitation of the C-C and C-N bonds of the ACN adsorbate molecules, and the threshold for the symmetric v1-stretch mode excitation of adsorbed NH3/ND3. Also, information about the temporal dynamics underlying the inelastic electron scattering was gained.