Source: https://www.icmm.csic.es/consolider-ingenio-astromol/?page_id=1613
Timestamp: 2019-04-25 22:20:11+00:00

Document:
October 2013 – AM-CSIC group: first ASTROMOL results with ALMA Cycle 0 observations in IRC+10216 (J. Cernicharo et al., accepted for publication in The Astrophysical Journal Letters).
September 2013 – GEM-UVA & AM-CSIC groups: New ASTROMOL high impact article on “Laboratory and astronomical discovery of hydromagnesium isocyanide” (C. Cabezas et al., The Astrophysical Journal).
August 6, 2013 – AM-CSIC group: New ASTROMOL high impact article on “Crystallization of CO2 ice and the absence of amorphous CO2 ice in space” (R. Escribano, G. Muñoz-Caro et al., PNAS – Proceedings of the National Academy of Sciences of the United States of America).
June 10, 2013 – AM-CSIC/MIC-OAN & GFM-CSIC groups: New ASTROMOL high impact article on “DETECTION OF THE AMMONIUM ION IN SPACE” (J. Cernicharo et al., The Astrophysical Journal Letters).
June 10, 2013 – GFM-CSIC and AM-CSIC/MIC-OAN groups: New ASTROMOL high impact article on “IMPROVED DETERMINATION OF THE 10 – 00 ROTATIONAL FREQUENCY OF NH3D+ FROM THE HIGH RESOLUTION SPECTRUM OF THE ν4 INFRARED BAND” (J. L. Domenech et al., The Astrophysical Journal Letters).
June 5, 2013 – GAPT-IAA group: New ASTROMOL high impact article on “LARGE ABUNDANCES OF POLYCYCLIC AROMATIC HYDROCARBONS IN TITAN’S UPPER ATMOSPHERE” (M. López-Puertas et al., The Astrophysical Journal).
 Detection of the Ammonium Ion in Space — Cernicharo, J.; Tercero, B.; Fuente, A.; Domenech, J. L.; Cueto, M.; Carrasco, E.; Herrero, V. J.; Tanarro, I.; Marcelino, N.; Roueff, E.; Gerin, M.; Pearson, J.
We report on the detection of a narrow feature at 262816.73 MHz towards Orion and the cold prestellar core B1-bS, that we attribute to the 10-00 line of the deuterated Ammonium ion, NH3D+. The observations were performed with the IRAM 30m radio telescope. The carrier has to be a light molecular species as it is the only feature detected over 3.6 GHz of bandwidth. The hyperfine structure is not resolved indicating a very low value for the electric quadrupolar coupling constant of Nitrogen which is expected for NH3D+ as the electric field over the N nucleus is practically zero. Moreover, the feature is right at the predicted frequency for the 10-00 transition of the Ammonium ion, 262817 ± 6 MHz (±3σ), using rotational constants derived from new infrared data obtained in our laboratory in Madrid. The estimated column density is (1.1 ± 0.2) x 1012 cm-2. Assuming a deuterium enhancement similar to that of NH2D, we derive N(NH4+) ≃ 2.6 x 1013 cm-2, i.e., an abundance for Ammonium of a few 10-11.
 Sensitive CO and 13CO survey of water fountain stars. Detections towards IRAS18460-0151 and IRAS18596+0315 — Rizzo, J. R.; Gomez, J. F.; Miranda, L. F.; Osorio, M.; Suarez, O.; Duran-Rojas, M. C.
Water fountain stars represent a stage between the asymptotic giant branch (AGB) and planetary nebulae phases, when the mass loss changes from spherical to bipolar. These types of evolved objects are characterized by high-velocity jets in the 22 GHz water maser emission. The objective of this work is to detect and study in detail the circumstellar gas in which the bipolar outflows are emerging. The detection and study of thermal lines may help in understanding the nature and physics of the envelopes in which the jets are developing. In two sources, IRAS 18460-0151 and IRAS 18596+0315, we identified wide velocity components with a width of 35 − 40 km s-1 that are centred at the stellar velocities. These wide components can be associated with the former AGB envelope of the progenitor star. A third case, IRAS 18286-0959, is reported as tentative. The molecular masses, mean densities, and mass-loss rates estimated for the circumstellar material associated with IRAS 18460-0151 and IRAS 18596+0315 confirm that these sources are at the end of the AGB or the beginning of the post-AGB evolutionary stages. The computed mass-loss rates are among the highest ones possible according to current evolutionary models, which leads us to propose that the progenitors of these water fountains had masses in the range from 4 to 8 M⊙. We speculate that CO emission is detected in water fountains as a result of a CO abundance enhancement caused by current episodes of low-collimation mass-loss.
 The IRAM-30 m line survey of the Horsehead PDR IV. Comparative chemistry of H2CO and CH3OH — Guzman, V. V.; Goicoechea, J. R.; Pety, J.; Gratier, P.; Gerin, M.; Roueff, E.; Le Petit, F.; Le Bourlot, J.; Faure, A.
Theoretical models and laboratory experiments show that CH3OH is efficiently formed on cold grain surfaces through the successive hydrogenation of CO, forming HCO and H2CO as intermediate species. In cold cores and low UV-field illumination photo-dissociation regions (PDRs) the ices can be released into the gas-phase through nonthermal processes such as photodesorption, which considerably increases their gas-phase abundances. We investigate the dominant formation mechanism of H2CO and CH3OH in the Horsehead PDR and its associated dense core. Pure gas-phase models cannot reproduce the observed abundances of either H2CO or CH3OH at the PDR position. The two species are therefore formed on the surface of dust grains and are subsequently photodesorbed into the gas-phase at this position. At the dense core, on the other hand, photodesorption of ices is needed to explain the observed abundance of CH3OH, while a pure gas-phase model can reproduce the observed H2CO abundance. Photodesorption is an efficient mechanism to release complex molecules in low-FUV-illuminated PDRs, where thermal desorption of ice mantles is ineffective.
 Detection of circumstellar nitric oxide – Enhanced nitrogen abundance in IRC+10420 — Quintana-Lacaci, G.; Agundez, M.; Cernicharo, J.; Bujarrabal, V.; Sanchez Contreras, C.; Castro-Carrizo, A.; Alcolea, J.
During a full line survey towards IRC +10420 in the 3 and 1 mm bands, we detected the emission of circumstellar nitric oxide for the first time. We aim to study the formation of NO and to confirm the enrichment of nitrogen expected for the most massive, evolved stars predicted by the hot bottom burning process. We have detected NO in a circumstellar envelope for the first time, along with a variety of N-rich molecules, which in turn shows that IRC +10420 presents a N-rich chemistry. Furthermore, we have found that to reproduce the observed NO line profiles, the initial abundance of nitrogen in the chemical model has to be increased by a factor 20 with respect to the values of the standard O-rich stars.
 Nitrogen isotopic ratios in Barnard 1: a consistent study of the N2H+, NH3, CN, HCN, and HNC isotopologues — Daniel, F.; Gerin, M.; Roueff, E.; Cernicharo, J.; Marcelino, N.; Lique, F.; Lis, D. C.; Teyssier, D.; Biver, N.; Bockelee-Morvan, D.
The 15N isotopologue abundance ratio measured today in different bodies of the solar system is thought to be connected to 15N-fractionation effects that would have occurred in the protosolar nebula. The present study aims at putting constraints on the degree of 15N-fractionation that occurs during the prestellar phase, through observations of D, 13C, and 15N-substituted isotopologues towards B1b. Molecules both from the nitrogen hydride family, i.e. N2H+, and NH3, and from the nitrile family, i.e. HCN, HNC, and CN, are considered in the analysis. Our modelling shows that all the molecules are affected by depletion onto dust grains in the region that encompasses the B1-bS and B1-bN cores. While high levels of deuterium fractionation are derived, we conclude that no fractionation occurs in the case of the nitrogen chemistry. Independently of the chemical family, the molecular abundances are consistent with 14N/15N ~ 300, a value representative of the elemental atomic abundances of the parental gas.
 The First Astrophysical Detection, Terahertz Spectrum, and Database for the Monodeuterated Species of Methyl Formate HCOOCH2D — Coudert, L. H.; Drouin, B. J.; Tercero, B.; Cernicharo, J.; Guillemin, J.-C.; Motiyenko, R. A.; Margules, L.
Based on new measurements carried out in the laboratory from 0.77 to 1.2 THz and on a line-frequency analysis of these new data, along with previously published data, we build a line list for HCOOCH2D that leads to its first detection in the Orion KL nebula. The observed lines, both in space and in the laboratory, involve the cis D-in-plane and trans D-out-of-plane conformations of HCOOCH2D and the two tunneling states arising from the large-amplitude motion connecting the two trans configurations. The model used in the line position calculation accounts for both cis and trans conformations, as well as the large-amplitude motion.
 SALT reveals the barium central star of the planetary nebula Hen 2-39 — Miszalski, B.; Boffin, H. M. J.; Jones, D.; Karakas, A. I.; Koeppen, J.; Tyndall, A. A.; Mohamed, S. S.; Rodriguez-Gil, P.; Santander-Garcia, M.
Classical barium stars are binary systems which consist of a late-type giant enriched in carbon and slow neutron capture (s-process) elements and an evolved white dwarf (WD) that is invisible at optical wavelengths. Here, we present evidence for a barium star in the PN Hen 2-39 (PN G283.8-04.2) as one of only a few known systems. An AGB star model of initial mass 1.8 M⊙ and a relatively large carbon pocket size can reproduce the observed abundances well, provided mass is transferred in a highly conservative way from the AGB star to the polluted star (e.g. wind Roche lobe overflow). It also shows signs of chromospheric activity and photometric variability with a possible rotation period of ˜5.5 d likely induced by wind accretion. The nebula exhibits an apparent ring morphology in keeping with the other PNe around barium stars (WeBo 1 and A 70) and shows a high degree of ionization implying the presence of an invisible hot pre-WD companion that will require confirmation with UV observations. In contrast to A 70, the nebular chemical abundance pattern is consistent with non-Type I PNe, in keeping with the trend found from nebular s-process studies that non-Type I PNe are more likely to be s-process enhanced.
 Soft X-Ray Irradiation of Methanol Ice: Formation of Products as a Function of Photon Energy — Chen, Y. -J.; Ciaravella, A.; Munoz Caro, G. M.; Cecchi-Pestellini, C.; Jimenez-Escobar, A.; Juang, K. -J.; Yih, T. -S.
Pure methanol ices have been irradiated with monochromatic soft X-rays of 300 and 550 eV close to the 1s resonance edges of C and O, respectively, and with a broadband spectrum (250-1200 eV). The infrared (IR) spectra of the irradiated ices show several new products of astrophysical interest such as CH2OH, H2CO, CH4, HCOOH, HCOCH2OH, CH3COOH, CH3OCH3, HCOOCH3, and (CH2OH)2, as well as HCO, CO, and CO2. The effect of X-rays is the result of the combined interactions of photons and electrons with the ice. A significant contribution to the formation and growth of new species in the CH3OH ice irradiated with X-rays is given by secondary electrons, whose energy distribution depends on the energy of X-ray photons. Within a single experiment, the abundances of the new products increase with the absorbed energy. Monochromatic experiments show that product abundances also increase with the photon energy. However, the abundances per unit energy of newly formed species show a marked decrease in the broadband experiment as compared to irradiations with monochromatic photons, suggesting a possible regulatory role of the energy deposition rate. The number of new molecules produced per absorbed eV in the X-ray experiments has been compared to those obtained with electron and ultraviolet (UV) irradiation experiments.
 Detection of a Noble Gas Molecular Ion, 36ArH+, in the Crab Nebula — Barlow, M. J.; Swinyard, B. M.; Owen, P. J.; Cernicharo, J.; Gomez, H. L.; Ivison, R. J.; Krause, O.; Lim, T. L.; Matsuura, M.; Miller, S.; Olofsson, G.; Polehampton, E. T.
Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5- and 1234.6-gigahertz J = 1-0 and 2-1 rotational lines of 36ArH+ at several positions in the Crab Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed 36ArH+ emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.
 Unveiling the dust nucleation zone of IRC+10216 with ALMA — Cernicharo, J.; Daniel, F.; Castro-Carrizo, A.; Agundez, M.; Marcelino, N.; Joblin, C.; Goicoechea, J. R.; Guelin, M.
We report the detection in IRC+10216 of lines of HNC J = 3 – 2 pertaining to nine excited vibrational states with energies up to ~5300 K. The spectrum, observed with ALMA, also shows a surprising large number of narrow, unidentified lines that arise in the vicinity of the star. The HNC data are interpreted through a 1D-spherical non-local radiative transfer model, coupled to a chemical model that includes chemistry at thermochemical equilibrium for the innermost regions and reaction kinetics for the external envelope. The derived abundance of HNC relative to H2 is 10–8 < χ(HNC) <10–6, and drops quickly where the gas density decreases and the gas chemistry is dominated by reaction kinetics. Merging HNC data with that of molecular species present throughout the inner envelope, such as vibrationally excited HCN, SiS, CS, or SiO, should allow us to characterize the physical and chemical conditions in the dust formation zone.
 HIFISTARS Herschel/HIFI observations of VY Canis Majoris. Molecular-line inventory of the envelope around the largest known star — Alcolea, J.; Bujarrabal, V.; Planesas, P.; Teyssier, D.; Cernicharo, J.; De Beck, E.; Decin, L.; Dominik, C.; Justtanont, K.; de Koter, A.; Marston, A. P.; Melnick, G.; Menten, K. M.; Neufeld, D. A.; Olofsson, H.; Schmidt, M.; Schoeier, F. L.; Szczerba, R.; Waters, L. B. F. M.
We detected the J = 6-5, J = 10-9, and J = 16-15 lines of 12CO and 13CO at ~100, 300, and 750 K above the ground state (and the 13CO J = 9-8 line). These lines are crucial for improving the modelling of the internal layers of the envelope around VY CMa. We also detected 27 lines of H2O and its isotopomers, and 96 lines of species such as NH3, SiO, SO, SO2 HCN, OH and others, some of them originating from vibrationally excited levels. Three lines were not unambiguously assigned. Our observations confirm that VY CMa’s envelope must consist of two or more detached components. The molecular excitation in the outer layers is significantly lower than in the inner ones, resulting in strong self-absorbed profiles in molecular lines that are optically thick in this outer envelope. Except for the most abundant species, CO and H2O, most of the molecular emission detected at these sub-mm/FIR wavelengths arise from the central parts of the envelope. The spectrum of VY CMa is very prominent in vibrationally excited lines, which are caused by the strong IR pumping present in the central regions. Compared with envelopes of other massive evolved stars, VY CMa’s emission is particularly strong in these vibrationally excited lines, as well as in the emission from less abundant species such as H13CN, SO, and NH3.
 Combined IRAM and Herschel/HIFI study of cyano(di)acetylene in Orion KL: tentative detection of DC3N — Esplugues, G. B.; Cernicharo, J.; Viti, S.; Goicoechea, J. R.; Tercero, B.; Marcelino, N.; Palau, A.; Bell, T. A.; Bergin, E. A.; Crockett, N. R.; Wang, S. Y.
We present a study of cyanoacetylene (HC3N) and cyanodiacetylene (HC5N) in Orion KL, through observations from two line surveys performed with the IRAM 30m telescope and the HIFI instrument on board the Herschel telescope. The frequency ranges covered are 80-280 GHz and 480-1906 GHz. We model the observed lines of HC3N, HC5N, their isotopologues (including DC3N), and vibrational modes, using a non-LTE radiative transfer code. This study (divided by families of molecules) is part of a global analysis of the physical conditions of Orion KL and the molecular abundances in the different components of this cloud. We detect 40 lines of the ground vibrational state of HC3N and 68 lines of its 13C isotopologues. We also detect 297 lines of six vibrational modes of this molecule (ν7, 2ν7, 3ν7, ν6, ν5, and ν6+ν7) and 35 rotational lines of the ground vibrational state of HC5N. We report the first tentative detection of DC3N in a giant molecular cloud. The high D/H ratio (similar to that obtained in cold clouds) that we derive suggests a deuterium enrichment. Our chemical models indicate that the possible deuterated HC3N in Orion KL is formed during the gas-phase. This fact provides new hints concerning the processes leading to deuteration.
 The IRAM-30 m line survey of the Horsehead PDR III. High abundance of complex (iso-)nitrile molecules in UV-illuminated gas — Gratier, P.; Pety, J.; Guzman, V.; Gerin, M.; Goicoechea, J. R.; Roueff, E.; Faure, A.
Complex (iso-)nitrile molecules, such as CH3CN and HC3N, are relatively easily detected in our Galaxy and in other galaxies. We constrain their chemistry through observations of two positions in the Horsehead edge: the photo-dissociation region (PDR) and the dense, cold, and UV-shielded core just behind it. We systematically searched for lines of CH3CN, HC3N, C3N, and some of their isomers in our sensitive unbiased line survey at 3, 2, and 1mm. We derived column densities and abundances through Bayesian analysis using a large velocity gradient radiative transfer model. The isomeric ratio CH3NC/CH3CN is 0.15+-0.02. In the case of CH3CN, pure gas phase chemistry cannot reproduce the amount of CH3CN observed in the UV-illuminated gas. We propose that CH3CN gas phase abundance is enhanced when ice mantles of grains are destroyed through photo-desorption or thermal-evaporation in PDRs, and through sputtering in shocks.
 ALMA observations of the Red Rectangle, a preliminary analysis — Bujarrabal, V.; Castro-Carrizo, A.; Alcolea, J.; Van Winckel, H.; Sanchez Contreras, C.; Santander-Garcia, M.; Neri, R.; Lucas, R.
We aim to study equatorial disks in rotation and axial outflows in post-AGB objects, as to disclose the formation and shaping mechanisms in planetary nebulae. So far, both disks and outflows had not been observed simultaneously. We have obtained high-quality ALMA observations of 12CO and 13CO J=3-2 and 12CO J=6-5 line emission in the Red Rectangle, the only post-AGB/protoplanetary object in which a disk in rotation has been mapped up to date. These observations provide an unprecedented description of the complex structure of this source. Together with an equatorial disk in rotation, we find a low-velocity outflow that occupies more or less the region placed between the disk and the optical X-shaped nebula. From our observations and preliminary modeling of the data, we confirm the previously known properties of the disk and obtain a first description of the structure, dynamics, and physical conditions of the outflow.
 Extended rotating disks around post-AGB stars — Bujarrabal, V.; Alcolea, J.; Van Winckel, H.; Santander-Garcia, M.; Castro-Carrizo, A.
There is a group of binary post-AGB stars that show a conspicuous NIR excess, usually assumed to arise from hot dust in very compact possibly rotating disks. These stars are surrounded by significantly fainter nebulae than the “standard”, well studied protoplanetary and planetary nebulae (PPNe, PNe). We present high-sensitivity mm-wave observations of CO lines in 24 objects of this type. CO emission is detected in most observed sources and the line profiles show that the emissions very probably come from disks in rotation. Estimates of the linear momenta carried by the outflows, which can only be performed in a few well studied objects, also yield moderate values, compared with the linear momenta that can be released by the stellar radiation pressure (contrary, again, to the case of the very massive and fast bipolar outflows in “standard” PPNe, that are strongly overluminous). The mass and dynamics of nebulae around various classes of post-AGB stars differ very significantly, and we can expect the formation of PNe with very different properties.
 Diagnostics of AGN-driven Molecular Outflows in ULIRGs from Herschel-PACS Observations of OH at 119um — Spoon, H. W. W.; Farrah, D.; Lebouteiller, V.; Gonzalez-Alfonso, E.; Bernard-Salas, J.; Urrutia, T.; Rigopoulou, D.; Westmoquette, M. S.; Smith, H. A.; Afonso, J.; Pearson, C.; Cormier, D.; Efstathiou, A.; Borys, C.; Verma, A.; Etxaluze, M.; Clements, D. L.
We report on our observations of the 79 and 119um doublet transitions of OH for 24 local (z<0.262) ULIRGs observed with Herschel-PACS as part of the Herschel ULIRG Survey (HERUS). Some OH119 profiles display a clear P-Cygni shape and therefore imply outflowing OH gas, other profiles are predominantly in absorption or are completely in emission. We find that the relative strength of the OH emission component decreases as the silicate absorption increases. This locates the OH outflows inside the obscured nuclei. The maximum outflow velocities for our sources range from less than 100 to 2000 km/s, with 15/24 (10/24) sources showing OH absorption at velocities exceeding 700 km/s (1000 km/s). We speculate that the molecular outflows in these sources may be in an early phase of disrupting the nuclear dust veil before these sources evolve into less obscured AGN. Four of our sources show high-velocity wings in their [C II] fine-structure line profiles implying neutral gas outflow masses of at least 2-4.5 x 108 solar masses.
 The Herschel/HIFI spectral survey of OMC-2 FIR 4 ( CHESS) An overview of the 480 to 1902 GHz range — Kama, M.; Lopez-Sepulcre, A.; Dominik, C.; Ceccarelli, C.; Fuente, A.; Caux, E.; Higgins, R.; Tielens, A. G. G. M.; Alonso-Albi, T.
A comparative analysis of the chemical inventories and physical processes and properties of protostars of various masses and evolutionary states is the goal of the Herschel CHEmical Surveys of Star forming regions (CHESS) key program. This paper focusses on the intermediate-mass protostar, OMC-2 FIR 4. We obtained a spectrum of OMC-2 FIR 4 in the 480 to 1902 GHz range with the HIFI spectrometer onboard Herschel and carried out the reduction, line identification, and a broad analysis of the line profile components, excitation, and cooling. We detect 719 spectral lines from 40 species and isotopologs. The line flux is dominated by CO, H2O, and CH3OH. The line profiles are complex and vary with species and upper level energy, but clearly contain signatures from quiescent gas, a broad component likely due to an outflow, and a foreground cloud. We find abundant evidence for warm, dense gas, as well as for an outflow in the field of view. A comparison with similar HIFI spectra of other sources is set to provide much new insight into star formation regions, a case in point being a difference of two orders of magnitude in the relative contribution of sulphur oxides to the line cooling of Orion KL and OMC-2 FIR 4.
 High-angular resolution observations towards OMC-2 FIR 4: Dissecting an intermediate-mass protocluster — Lopez-Sepulcre, A.; Taquet, V.; Sanchez-Monge, A.; Ceccarelli, C.; Dominik, C.; Kama, M.; Caux, E.; Fontani, F.; Fuente, A.; Ho, P. T. P.; Neri, R.; Shimajiri, Y.
Intermediate-mass stars are an important ingredient of our Galaxy and a key to understanding how high- and low-mass stars form in clusters. One of the closest known young intermediate-mass protoclusters is OMC-2 FIR 4, which is located at a distance of 420 pc in Orion. This region is one of the few where the complete 500–2000 GHz spectrum has been observed with the heterodyne spectrometer HIFI on board the Herschel satellite, and unbiased spectral surveys at 0.8, 1, 2, and 3 mm have been obtained with the JCMT and IRAM 30-m telescopes. We aim to disentangle the core multiplicity, to investigate the morphology of this region in order to study the formation of a low- and intermediate-mass protostar cluster, and to aid in interpretation of the single-dish line profiles already in our hands. Our interferometric observations show the complexity of the intermediate-mass protocluster OMC-2 FIR 4, where multiple cores, chemical differentiation, and an ionised region all coexist within an area of only 10 000 AU.
 Observing extended sources with the Herschel SPIRE Fourier Transform Spectrometer — Wu, R.; Polehampton, E. T.; Etxaluze, M.; Makiwa, G.; Naylor, D. A.; Salji, C.; Swinyard, B. M.; Ferlet, M.; van der Wiel, M. H. D.; Smith, A. J.; Fulton, T.; Griffin, M. J.; Baluteau, J. -P.; Benielli, D.; Glenn, J.; Hopwood, R.; Imhof, P.; Lim, T.; Lu, N.; Panuzzo, P.; Pearson, C.; Sidher, S.; Valtchanov, I.
The Spectral and Photometric Imaging Receiver (SPIRE) on the European Space Agency’s Herschel Space Observatory utilizes a pioneering design for its imaging spectrometer in the form of a Fourier Transform Spectrometer (FTS). The standard FTS data reduction and calibration schemes are aimed at objects with either a spatial extent that is much larger than the beam size or a source that can be approximated as a point source within the beam. However, when sources are of intermediate spatial extent, neither of these calibrations schemes is appropriate and both the spatial response of the instrument and the source’s light profile must be taken into account and the coupling between them explicitly derived. To that end, we derive the necessary corrections using an observed spectrum of a fully extended source with the beam profile and considering the source’s light profile. We apply the derived correction to several observations of planets and compare the corrected spectra with their spectral models to study the beam coupling efficiency of the instrument in the case of partially extended sources. We find that we can apply these correction factors for sources with angular sizes up to θD ~ 17′′. Using this technique on an observation of Saturn, we estimate a size of 17.2′′, which is 3% larger than its true size on the day of observation. Finally, we show the results of the correction applied on observations of a nearby galaxy, M82, and the compact core of a Galactic molecular cloud, Sgr B2.
 A line confusion-limited millimeter survey of Orion KL III. Sulfur oxide species — Esplugues, G. B.; Tercero, B.; Cernicharo, J.; Goicoechea, J. R.; Palau, A.; Marcelino, N.; Bell, T. A.
We present a study of the sulfur-bearing species detected in a line confusion-limited survey towards Orion KL performed with the IRAM 30-m telescope in the frequency range 80−281 GHz. This study is part of an analysis of the line survey divided into families of molecules. Our aim is to derive accurate physical conditions, as well as molecular abundances, in the different components of Orion KL from observed SO and SO2 lines. The highest column densities for SO and SO2 are found in the high-velocity plateau (a region dominated by shocks) and in the hot core. These values are up to three orders of magnitude higher than the results for the ridge components. We also find high column densities for their isotopologues in both components. Therefore, we conclude that SO and SO2 are good tracers, not only of regions affected by shocks, but also of regions with warm dense gas (hot cores).
 Crystallization of CO2 ice and the absence of amorphous CO2 ice in space — Escribano, R.; Muñoz Caro, G. M.; Cruz-Díaz, G. A.; Rodríguez-Lazcano, Y.; Maté, B.
The amount of CO2 in ice mantles and the presence of pure CO2 ice are significant indicators of the temperature history of dust in protostars. It is therefore important to know if CO2 is mixed with other molecules in the ice matrix or segregated and whether it is present in an amorphous or crystalline form. We apply a multidisciplinary approach involving IR spectroscopy in the laboratory, theoretical modeling of solid structures, and comparison with astronomical observations. We generate an unprecedented highly amorphous CO2 ice and study its crystallization both by thermal annealing and by slow accumulation of monolayers from the gas phase under an ultrahigh vacuum. Structural changes are followed by IR spectroscopy. We also devise theoretical models to reproduce different CO2 ice structures. We detect a preferential in-plane orientation of some vibrational modes of crystalline CO2. We identify the IR features of amorphous CO2 ice, and, in particular, we provide a theoretical explanation for a band at 2,328 cm-1 that dominates the spectrum of the amorphous phase and disappears when the crystallization is complete. Our results allow us to rule out the presence of pure and amorphous CO2 ice in space based on the observations available so far, supporting our current view of the evolution of CO2 ice.
 Discovery of Methyl Acetate and Gauche Ethyl Formate in Orion — Tercero, B.; Kleiner, I.; Cernicharo, J.; Nguyen, H. V. L.; Lopez, A.; Munoz Caro, G. M.
We report on the discovery of methyl acetate, CH3COOCH3, through the detection of a large number of rotational lines from each one of the spin states of the molecule: AA species (A1 or A2), EA species (E1), AE species (E2), EE species (E3 or E4). We also report the detection, for the first time in space, of the gauche conformer of ethyl formate, CH3CH2OCOH, in the same source. The trans conformer is also detected for the first time outside the galactic center source SgrB2. From the derived velocity of the emission of methyl acetate we conclude that it arises mainly from the compact ridge region with a total column density of (4.2±0.5)x1015 cm-2. The derived rotational temperature is 150 K. The column density for each conformer of ethyl formate, trans and gauche, is (4.5±1.0)x1014 cm-2. Their abundance ratio indicates a kinetic temperature of 135 K for the emitting gas and suggests that gas phase reactions could participate efficiently in the formation of both conformers in addition to cold ice mantle reactions on the surface of dust grains.
 Cores, filaments, and bundles: hierarchical core formation in the L1495/B213 Taurus region — Hacar, A.; Tafalla, M.; Kauffmann, J.; Kovacs, A.
We have studied the 10 pc-long L1495/B213 complex in Taurus to investigate how dense cores have condensed out of the lower-density cloud material. Conclusions: Core formation in L1495/B213 has proceeded by hierarchical fragmentation. The cloud fragmented first into several pc-scale regions. Each of these regions later fragmented into velocity-coherent filaments of about 0.5 pc in length. Finally, a small number of these filaments fragmented quasi-statically and produced the individual dense cores we see today.
Garcia-Burillo, S.; Le Petit, F.; Le Bourlot, J.
We study the chemistry of small hydrocarbons in the photon-dominated regions (PDRs) associated with the ultra-compact HII region Mon R2. Our goal is to determine the variations of the abundance of small hydrocarbons in a high-UV irradiated PDR and investigate their chemistry. We present an observational study of CH, CCH and c-C3H2 in Mon R2 combining data obtained with the IRAM 30m telescope and Herschel. We determine the column densities of these species, and compare their spatial distributions with that of polycyclic aromatic hydrocarbon (PAH). We compare the observational results with different chemical models to explore the relative importance of gas-phase, grain-surface and time-dependent chemistry in these environments. Our study shows that CCH and c-C3H2 present a complex chemistry in which UV photons, grain-surface chemistry and time dependent effects contribute to determine their abundances.
 Non-local radiative transfer in strongly inverted masers — Daniel, F.; Cernicharo, J.
We present a numerical method that enables us to obtain self-consistent solutions for both the statistical equilibrium and radiative transfer equations. Using the standard maser theory, the method of Short Characteristics is extended to obtain the solution of the integro-differential radiative transfer equation, appropriate to the case of intense masing lines. We have applied our method to the maser lines of the H2O molecule and we compare with the results obtained with a less accurate approach. In the regime of large maser opacities we find large differences in the intensity of the maser lines that could be as high as several orders of magnitude. The comparison between the two methods shows, however, that the effect on the thermal lines is modest. Finally, the effect introduced by rate coefficients on the prediction of H2O masing lines and opacities is discussed, making use of various sets of rate coefficients involving He, o-H2 and p-H2. We find that the masing nature of a line is not affected by the selected collisional rates. However, from one set to the other the modelled line opacities and intensities can vary by up to a factor ~2 and ~10 respectively.
 Probing the role of Polycyclic Aromatic Hydrocarbons in the photoelectric heating within photodissociation regions — Okada, Y.; Pilleri, P.; Berne, O.; Ossenkopf, V.; Fuente, A.; Goicoechea, J. R.; Joblin, C.; Kramer, C.; Roellig, M.; Teyssier, D.; van der Tak, F. F. S.
We observationally investigate the relation between the photoelectric heating efficiency in PDRs and the charge of PAHs, which are considered to play a key role in photoelectric heating. Using PACS onboard Herschel, we observed six PDRs spanning a wide range of FUV radiation fields. To measure the photoelectric heating efficiency, we obtained the intensities of the main cooling lines as well as the FIR continuum intensity. We used Spitzer/IRS spectroscopic mapping observations to investigate the MIR PAH features in the same regions. We decomposed the MIR PAH emission into that of neutral (PAH0) and positively ionized (PAH+) species to derive the fraction of the positively charged PAHs, and compare it to the photoelectric heating efficiency. All positions with a high PAH+ fraction show a low heating efficiency, and all positions with a high heating efficiency have a low PAH+ fraction, supporting the scenario in which a positive grain charge results in a decreased heating efficiency.
Far-infrared Herschel-PACS spectra of 18 low-mass protostars of various luminosities and evolutionary stages are studied in the context of the WISH key program. For most targets, the spectra include many wavelength intervals selected to cover specific CO, H2O, OH, and atomic lines. For four targets the spectra span the entire 55-200 mu m region. The PACS data probe at least two physical components. The H2O and CO emission very likely arises in non-dissociative (irradiated) shocks along the outflow walls with a range of pre-shock densities. Some OH is also associated with this component, most likely resulting from H2O photodissociation. UV-heated gas contributes only a minor fraction to the CO emission observed by PACS, based on the strong correlation between the shock-dominated CO 24-23 line and the CO 14-13 line. [O I] and some of the OH emission probe dissociative shocks in the inner envelope. The total far-infrared cooling is dominated by H2O and CO, with the fraction contributed by [O I] increasing for Class I sources. Consistent with previous studies, the ratio of total far-infrared line emission over bolometric luminosity decreases with the evolutionary state.
We aim to study the excitation conditions of the molecular gas in the rotating disk of the Red Rectangle, the only post-asymptotic-giant-branch object in which the existence of an equatorial rotating disk has been demonstrated. We present far-infrared Herschel/HIFI observations of the (CO)-C-12 and (CO)-C-13 J = 6-5, J = 10-9, and J = 16-15 transitions in the Red Rectangle. We also present our code in detail and discuss the accuracy of its predictions, from comparison with well-tested codes. Theoretical line profiles are compared with the empirical data to deduce the physical conditions in the disk by means of model fitting. We conclude that our code is very efficient and produces reliable results. The comparison of the theoretical predictions with our observations reveals that the temperature of the Red Rectangle disk is typically similar to 100-150 K, about twice as high as previously deduced from mm-wave observations of lower-J lines. We discuss the relevance of these new temperature estimates for understanding the thermodynamics and dynamics of this prototype object, as well as for interpreting observations of other rarely studied post-AGB disks. Despite our sophisticated treatment of the line formation, our model cannot explain the relatively strong line-wing emission for intermediate-J transitions. We argue that a model including a rotating disk only cannot reproduce these data and suggest that there is an additional extended (probably bipolar) structure expanding at about 7-15 km s-1.
A small group of bipolar protostellar outflows display strong emission from shock-tracer molecules such as SiO and CH3OH, and are generally referred to as “chemically active”. The best-studied outflow from this group is the one in L 1157. We study the molecular emission from the bipolar outflow powered by the very young stellar object HH 114 MMS and compare its chemical composition with that of the L 1157 outflow. We have used the IRAM 30 m radio telescope to observe a number of transitions from CO, SiO, CH3OH, SO, CS, HCN, and HCO+ toward the HH 114 MMS outflow. The observations consist of maps and a two-position molecular survey. The HH 114 MMS outflow presents strong emission from a number of shock-tracer molecules that dominate the appearance of the maps around the central source. The abundance of these molecules is comparable to the abundance in L 1157. The outflow from HH 114 MMS is a spectacular new case of a chemically active outflow.
 Herschel Far-infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near Sgr A* — Goicoechea, J. R.; Etxaluze, M.; Cernicharo, J.; Gerin, M.; Neufeld, D. A.; Contursi, A.; Bell, T. A.; De Luca, M.; Encrenaz, P.; Indriolo, N.; Lis, D. C.; Polehampton, E. T.; Sonnentrucker, P.
 High-pressure, low-abundance water in bipolar outflows. Results from a Herschel-WISH survey — Tafalla, M.; Liseau, R.; Nisini, B.; Bachiller, R.; Santiago-Garcia, J; van Dishoeck, E. F.; Kristensen, L. E.; Herczeg, G. J.; Yildiz, U. A.
A survey of the water emission in a sample of more than 20 outflows from low-mass young stellar objects is presented with the goal of characterizing the physical and chemical conditions of the emitting gas. We used the HIFI and PACS instruments on board the Herschel Space Observatory to observe the two fundamental lines of ortho-water at 557 and 1670 GHz. A warm origin of the water emission is confirmed by a remarkable correlation between the intensities of the 557 and 1670 GHz lines, which also indicates that the emitting gas has a narrow range of excitations. A radiative transfer analysis shows that while there is some ambiguity in the exact combination of density and temperature values. Our data challenge current C-shock models of water production through the combination of wing-line profiles, high gas compressions, and low abundances.
 Prebiotic chemistry in icy grain mantles in space. An experimental and observational approach — Muñoz-Caro, G. M.; Dartois, E.
A compendium of different solid carbonaceous materials detected in space is presented, focussing on the search for organic matter of prebiotic interest. This journey takes us from the carbon grains likely formed in the atmospheres of evolved stars to organic grain mantles made from ice processing thought to be present in dense interstellar clouds and circumstellar regions, making a stop in solar system objects that could have delivered organic species to the early Earth. The most abundant carbon materials detected to date in space appear to be of little biological relevance. On the other hand, organic refractory residues, made in the laboratory from UV-photoprocessing followed by warm-up of interstellar ice analogs, are a hydrocarbon material rich in O and N containing chemical compounds that could act as initiators of prebiotic chemistry. A similar material might be present in dust grains inside dense clouds or circumstellar regions, some comets, and as a minor component in carbonaceous chondrites. We use infrared spectroscopy as a tool to spot organic refractory matter in various space environments. The delivery of organic materials via comets, (micro-) meteorites, and interplanetary dust particles to the primitive Earth might have contributed as a starting material for prebiotic chemistry. To test this hypothesis, it is first essential to characterize the composition of exogenous organic matter.
 A complete model of CH+ rotational excitation including radiative and chemical pumping processes — Godard, B.; Cernicharo, J.
Excitation of far-infrared and submillimetric molecular lines may originate from nonreactive collisions, chemical formation, or far infrared, near-infrared, and optical fluorescences. As a template, we investigate the impact of each of these processes on the excitation of the methylidyne cation CH+ and on the intensities of its rotational transitions recently detected in emission in dense photodissociation regions (PDRs) and in planetary nebulae. We have developed a nonlocal thermodynamic equilibrium excitation model that includes the entire energy structure of CH+, i.e. taking into account the pumping of its vibrational and bound and unbound electronic states by near-infrared and optical photons. The model includes the theoretical cross-sections of nonreactive collisions with H, H2 , He, and e− , and a Boltzmann distribution is used to describe the probability of populating the excited levels of CH+ during its chemical formation by hydrogenation of C+. Our results point towards interstellar and circumstellar media with densities lower than previously established and cast doubts on the clumpiness of well-studied molecular clouds.
 The chemistry of ions in the Orion Bar I. – CH+, SH+, and CF+. The effect of high electron density and vibrationally excited H2 in a warm PDR surface — Nagy, Z.; Van der Tak, F. F. S.; Ossenkopf, V.; Gerin, M.; Le Petit, F.; Le Bourlot, J.; Black, J. H.; Goicoechea, J. R.; Joblin, C.; Röllig, M.; Bergin, E. A.
The abundances of interstellar CH+ and SH+ are not well understood as their most likely formation channels are highly endothermic. Several mechanisms have been proposed to overcome the high activation barriers, including shocks, turbulence, and H2 vibrational excitation. Using data from the Herschel Space Observatory, we studied the formation of ions, in particular CH+ and SH+ in a typical high UV-illumination warm and dense photon-dominated region (PDR), the Orion Bar. An analytic approximation and a numerical comparison to PDR models indicate that the internal vibrational energy of H2 can explain the formation of CH+ for typical physical conditions in the Orion Bar near the ionization front. The formation of SH+ is also likely to be explained by H2 vibrational excitation. The abundance ratios of CH+ and SH+ trace the destruction paths of these ions, and indirectly, the ratios of H, H2, and electron abundances as a function of depth into the cloud.
 Herschel/HIFI observations of [C II] and [13C II] in photon-dominated regions — Ossenkopf, V.; Röllig, M.; Neufeld, D. A.; Pilleri, P.; Lis, D. C.; Fuente, A.; van der Tak, F. F. S.; Bergin, E.
Recently, we have introduced detailed isotopic chemistry into the KOSMA-τ model for photon-dominated regions (PDRs), which allows calculating abundances of carbon isotopologues as a function of PDR parameters. Radiative transfer computations then allow to predict the observed [C ii]/[13C ii] line intensity ratio for specific geometries. Here, we compare these model predictions with new Herschel observations. Carbon fractionation can be significant even in relatively warm PDRs, but a resulting enhanced [C ii]/[13C ii] intensity ratio is only observable for special configurations. In most cases, a reduced [C ii]/[13C ii] intensity ratiocan be used instead to derive the [C ii] optical depth, leading to reliable column density estimates that can be compared with PDR model predictions. The C+ column densities show that, for all sources, at the position of the [C ii] peak emission, the dominant fraction of the gas-phase carbon is in the form of C+.
 Fueling the central engine of radio galaxies. II. The footprints of AGN feedback on the ISM of 3C 236 — Labiano, A.; García-Burillo, S.; Combes, F.; Usero, A.; Soria-Ruiz, R.; Tremblay, G.; Neri, R.; Fuente, A.; Morganti, R.; Oosterloo, T.
There is growing observational evidence of active galactic nuclei (AGN) feedback on the interstellar medium (ISM) of radio-quiet and radio-loud galaxies. While AGN feedback is expected to be more common at high-redshift objects, studying local universe galaxies helps to better characterize the different manifestations of AGN feedback. The IRAM Plateau de Bure interferometer (PdBI) was used to study the distribution and kinematics of molecular gas in 3C 236 by imaging with high spatial resolution (0.6 arcsec) the emission of the 2–1 line of 12CO in the nucleus of the galaxy. We searched for outflow signatures in the CO map. There are no signs of ongoing AGN feedback to the molecular ISM of 3C 236. The recent reactivation of the AGN in 3C 236 (about 105 yr ago) is a likely explanation for the early evolutionary status of its molecular disk.
 Early Stages of Cluster Formation: Fragmentation of Massive Dense Cores down to ~ 1000 AU — Palau, A.; Fuente, A.; Girart, J. M.; Estalella, R.; Ho, P. T. P.; Sánchez-Monge, Á.; Fontani, F.; Busquet, G.; Commerçon, B.; Hennebelle, P.; Boissier, J.; Zhang, Q.; Cesaroni, R.; Zapata, L. A.
In order to study the fragmentation of massive dense cores, which constitute the cluster cradles, we observed the continuum at 1.3 mm and the CO (2-1) emission of four massive cores with the Plateau de Bure Interferometer in the most extended configuration. We compiled a list of properties for the 18 massive dense cores, such as bolometric luminosity, total mass, and mean density, and found no correlation of any of these parameters with the fragmentation level. In order to investigate the combined effects of the magnetic field, radiative feedback, and turbulence in the fragmentation process, we compared our observations to radiation magnetohydrodynamic simulations and found that the low-fragmented regions are reproduced well in the magnetized core case, while the highly fragmented regions are consistent with cores where turbulence dominates over the magnetic field. Overall, our study suggests that the fragmentation in massive dense cores could be determined by the initial magnetic field/turbulence balance in each particular core.
 IRAS 19520+2759: a 105 L massive young stellar object driving a collimated outflow — Palau, A.; Sánchez Contreras, C.; Sahai, R.; Sánchez-Monge, Á.; Rizzo, J. R.
The theory of massive star formation currently suffers from a scarce observational base of massive young stellar objects to compare with. In this paper, we present interferometric 12CO (1–0), 13CO (1–0), C18O (1–0) and 2.6 mm 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. 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.
 Water Absorption in Galactic Translucent Clouds: Conditions and History of the Gas Derived from Herschel/HIFI PRISMAS Observations — Flagey, N.; Goldsmith, P. F.; Lis, D. C.; Gerin, M.; Neufeld, D.; Sonnentrucker, P.; De Luca, M.; Godard, B.; Goicoechea, J. R.; Monje, R.; Phillips, T. G.
We present Herschel/HIFI observations of the three ground state transitions of H2O (556, 1669, and 1113 GHz) and H218O (547, 1655, and 1101 GHz)—as well as the first few excited transitions of H2O (987, 752, and 1661 GHz)—toward six high-mass star-forming regions, obtained as part of the PRISMAS (PRobing InterStellar Molecules with Absorption line Studies) Guaranteed Time Key Program. Water vapor associated with the translucent clouds in Galactic arms is detected in absorption along every line of sight in all the ground state transitions. We derive the water ortho-to-para ratio for each absorption feature along the line of sight and find that most of the clouds show ratios consistent with the value of 3 expected in thermodynamic equilibrium in the high-temperature limit. However, two clouds with large column densities exhibit a ratio that is significantly below 3. This may argue that the history of water molecules includes a cold phase, either when the molecules were formed on cold grains in the well-shielded, low-temperature regions of the clouds, or when they later become at least partially thermalized with the cold gas (~25 K) in those regions.
 Herschel CHESS discovery of the fossil cloud that gave birth to the Trapezium and Orion KL — López-Sepulcre, A.; Kama, M.; Ceccarelli, C.; Dominik, C.; Caux, E.; Fuente, A.; Alonso-Albi, T.
As part of the Herschel guaranteed time key programme CHESS, we present the discovery of a diffuse gas component in the foreground of the intermediate-mass protostar OMC-2 FIR 4, located in the Orion A region. Making use of the full HIFI spectrum of OMC-2 FIR 4 obtained in CHESS, we detected several ground-state lines from OH+ , H2O+ , HF, and CH+ , all of them seen in absorption against the dust continuum emission of the protostar’s envelope. We derived column densities for each species, as well as an upper limit to the column density of the undetected H3O+. We conclude that the foreground cloud we detected is an extension of the C+ interface seen in the direction of Orion KL, and interpret it to be the remains of the parental cloud of OMC-1, which extends from OMC-1 up to OMC-2.
 Herschel Observations Reveal Anomalous Molecular Abundances toward the Galactic Center — Sonnentrucker, P.; Neufeld, D. A.; Gerin, M.; De Luca, M.; Indriolo, N.; Lis, D. C.; Goicoechea, J. R.
We report the Herschel detections of hydrogen fluoride (HF) and para-water (p-H2O) in gas intercepting the sight lines to two well-studied molecular clouds in the vicinity of the Sgr A complex. We find that the HF and water abundances are consistent with those measured toward other sight lines probing the Galactic disk gas. Comparison with CH data indicates that our observations are consistent with a picture where HF and a fraction of the H2O absorption arise in diffuse molecular clouds showing Galactic disk-like abundances while the bulk of the water absorption arises in warmer (T ≥ 400 K) diffuse molecular gas.
 Three-dimensional Martian ionosphere model: I. The photochemical ionosphere below 180 km — Gonzalez-Galindo, F.; Chaufray, J. Y.; Lopez-Valverde, M. A.; Gilli, G.; Forget, F.; Leblanc, F.; Modolo, R.; Hess, S.; Yagi, M.
We describe the Mars ionosphere with unprecedented detail in 3-D, as simulated by a Mars general circulation model (the Laboratoire de Meteorologie Dynamique Mars GCM), and compare it with recent measurements. The model includes a number of recent extensions and improvements. Different simulations for a full Martian year have been performed. The electron density at the main ionospheric peak is shown to vary with the Sun-Mars distance and with the solar variability, both in the long-term (11 year solar cycle) and on shorter temporal scales (solar rotation). The main electronic peak is shown to be located at the same pressure level during all the Martian year. As a consequence, its altitude varies with latitude, local time, and season according to the natural expansions and fluctuations of the neutral atmosphere, in agreement with previous models. The model predicts a nighttime ionosphere due only to photochemistry. The simulated ionosphere close to the evening terminator is in agreement with observations. No effort has been made to explain the patchy ionosphere observed in the deep nightside. We have compared the modeled ionosphere with Mars Global Surveyor and Mars Advanced Radar for Subsurface and Ionosphere Sounding data. The model reproduces the solar zenith angle variability of the electron density and the altitude of the peak, although it underestimates the electron density at the main peak by about 20%. The electron density at the secondary peak is strongly underestimated by the model, probably due to a very crude representation of the X-ray solar flux. This is one of the aspects that needs a revision in future versions of the model.
 Large abundances of Polycyclic Aromatic Hydrocarbons in Titan’s upper atmosphere — López-Puertas, M.; Dinelli, B. M.; Adriani, A.; Funke, B.; García-Comas, M.; Moriconi, M. L.; D’Aversa, E.; Boersma, C.; Allamandola, L. J.
In this paper, we analyze the strong unidentified emission near 3.28 μm in Titan’s upper daytime atmosphere recently discovered by Dinelli et al. We have studied it by using the NASA Ames PAH IR Spectroscopic Database. The polycyclic aromatic hydrocarbons (PAHs), after absorbing UV solar radiation, are able to emit strongly near 3.3 μm. By using current models for the redistribution of the absorbed UV energy, we have explained the observed spectral feature and have derived the vertical distribution of PAH abundances in Titan’s upper atmosphere. PAHs have been found to be present in large concentrations, about (2-3) × 104 particles cm–3. The identified PAHs have 9-96 carbons, with a concentration-weighted average of 34 carbons. The mean mass is ~430 u; the mean area is about 0.53 nm2; they are formed by 10-11 rings on average, and about one-third of them contain nitrogen atoms. Recently, benzene together with light aromatic species as well as small concentrations of heavy positive and negative ions have been detected in Titan’s upper atmosphere. We suggest that the large concentrations of PAHs found here are the neutral counterpart of those positive and negative ions, which hence supports the theory that the origin of Titan main haze layer is located in the upper atmosphere.
 An unidentified emission in Titan’s upper atmosphere — Dinelli, B. M.; López-Puertas, M.; Adriani, A.; Moriconi, M. L.; Funke, B.; García-Comas, M.; D’Aversa, E.
We have analyzed limb daytime observations of Titan’s upper atmosphere at 3.3 μm, acquired by the visual-infrared mapping spectrometer (VIMS) on Cassini. They were previously studied by García-Comas et al. (2011) to derive CH4 densities. Here, we report an unidentified emission peaking around 3.28 μm, hidden under the methane R branch. This emission is very strong, with intensity comparable to the CH4 bands located in the same spectral region. It presents a maximum at about 950 km and extends from 600 km up to 1250 km. It is definitely pumped by solar radiation since it vanishes at night. Our analysis shows that neither methane nor the major hydrocarbon compounds already discovered in Titan’s upper atmosphere are responsible for it. We have discarded many other potential candidates and suggest that the unidentified emission might be caused by aromatic compounds.
 A three-dimensional multilevel radiative transfer code for modeling the intensity and polarization of spectral lines with massively parallel computers — Stepan, J.; Bueno, J. T.
The interpretation of the intensity and polarization of the spectral line radiation produced in the atmosphere of the Sun and of other stars requires solving a radiative transfer problem that can be very complex, especially when the main interest lies in modeling the spectral line polarization produced by scattering processes and the Hanle and Zeeman effects. One of the difficulties is that the plasma of a stellar atmosphere can be highly inhomogeneous and dynamic, which implies the need to solve the non-equilibrium problem of the generation and transfer of polarized radiation in realistic three-dimensional (3D) stellar atmospheric models. Here we present PORTA, an efficient multilevel radiative transfer code we have developed for the simulation of the spectral line polarization caused by scattering processes and the Hanle and Zeeman effects in 3D models of stellar atmospheres. Another crucial feature of PORTA is its parallelization strategy, which allows us to speed up the numerical solution of complicated 3D problems by several orders of magnitude with respect to sequential radiative transfer approaches, given its excellent linear scaling with the number of available processors. The PORTA code can also be conveniently applied to solve the simpler 3D radiative transfer problem of unpolarized radiation in multilevel systems.
 Improved Search of Principal Component Analysis Databases for Spectro-Polarimetric Inversion — Casini, R.; Asensio-Ramos, A.; Lites, B. W.; Ariste, A. L.
We describe a simple technique for the acceleration of spectro-polarimetric inversions based on principal component analysis (PCA) of Stokes profiles. This technique involves the indexing of the database models based on the sign of the projections (PCA coefficients) of the first few relevant orders of principal components of the four Stokes parameters. In this way, each model in the database can be attributed a distinctive binary number of 24n bits, where n is the number of PCA orders used for the indexing. Each of these binary numbers (indexes) identifies a group of “compatible” models for the inversion of a given set of observed Stokes profiles sharing the same index. The complete set of the binary numbers so constructed evidently determines a partition of the database. The search of the database for the PCA inversion of spectro-polarimetric data can profit greatly from this indexing. In practical cases it becomes possible to approach the ideal acceleration factor of 24n as compared to the systematic search of a non-indexed database for a traditional PCA inversion. This indexing method relies on the existence of a physical meaning in the sign of the PCA coefficients of a model. For this reason, the presence of model ambiguities and of spectro-polarimetric noise in the observations limits in practice the number n of relevant PCA orders that can be used for the indexing.
 Coronal loop physical parameters from the analysis of multiple observed transverse oscillations — Asensio Ramos, A.; Arregui, I.
The analysis of quickly damped transverse oscillations of solar coronal loops using magneto-hydrodynamic seismology allow us to infer physical parameters that are difficult to measure otherwise. Under the assumption that such damped oscillations are due to the resonant conversion of global modes into Alfven oscillations of the tube surface, we carry out a global seismological analysis of a large set of coronal loops. A Bayesian hierarchical method is used to obtain distributions for coronal loop physical parameters by means of a global analysis of a large number of observations. The resulting distributions summarise global information and constitute data-favoured information that can be used for the inversion of individual events. The results strongly suggest that internal Alfven travel times along the loop are larger than 100 s and smaller than 540 s with 95% probability. Likewise, the density contrast between the loop interior and the surrounding is larger than 2.3 and below 6.9 with 95% probability.
 A PCA approach to stellar effective temperatures — Munoz Bermejo, J.; Asensio Ramos, A.; Allende Prieto, C.
We explore a new approach in which the spectrum is used to characterize a star’s effective temperature based on a calibration established by a small set of standard stars. We perform principal component analysis on homogeneous libraries of stellar spectra, then calibrate a relationship between the principal components and the effective temperature using a set of stars with reliable effective temperatures. We find that our procedure gives excellent consistency when spectra from a homogeneous set of observations are used. Systematic offsets may appear when combining observations from different sources. Using as reference the spectra of stars with high-quality spectroscopic temperatures in the Elodie library, we define a temperature scale for FG-type disk dwarfs with an internal consistency of about 50 K, in excellent agreement with temperatures from direct determinations, but distinct from widely used scales based on the infrared flux method.
 Determination of Transverse Density Structuring from Propagating Magnetohydrodynamic Waves in the Solar Atmosphere — Arregui, I.; Asensio Ramos, A.; Pascoe, D. J.
We present a Bayesian seismology inversion technique for propagating magnetohydrodynamic (MHD) transverse waves observed in coronal waveguides. The technique uses theoretical predictions for the spatial damping of propagating kink waves in transversely inhomogeneous coronal waveguides. It combines wave amplitude damping length scales along the waveguide with theoretical results for resonantly damped propagating kink waves to infer the plasma density variation across the oscillating structures. Provided the spatial dependence of the velocity amplitude along the propagation direction is measured and the existence of two different damping regimes is identified, the technique would enable us to fully constrain the transverse density structuring, providing estimates for the density contrast and its transverse inhomogeneity length scale.
 Isotropic inelastic and superelastic collisional rates in a multiterm atom — Belluzzi, L.; Landi Degl’Innocenti, E.; Trujillo Bueno, J.
In this paper we formally define and investigate the transfer and relaxation rates due to isotropic inelastic and superelastic collisions that enter the statistical equilibrium equations for the atomic density matrix of a multiterm atom. Under the hypothesis that the interaction between the collider and the atom can be described by a dipolar operator, we provide expressions that relate the collisional rates for interference between different J-levels to the usual collisional rates for J-level populations, for which experimental data or approximate theoretical expressions are generally available. We show that the rates for populations and interference within the same J-level reduce to those previously obtained for the multilevel model atom (where quantum interference is assumed to be present only between magnetic sublevels pertaining to any given J-level). Finally, we apply the general equations to the case of a two-term atom with unpolarized lower term, illustrating the impact of inelastic and superelastic collisions on the scattering line polarization through radiative transfer calculations in a slab of stellar atmospheric plasma anisotropically illuminated by the photospheric radiation field.
 Bayesian Analysis of Multiple Harmonic Oscillations in the Solar Corona — Arregui, I.; Asensio Ramos, A.; Díaz, A. J.
The detection of multiple mode harmonic kink oscillations in coronal loops enables to obtain information on coronal density stratification and magnetic field expansion using seismology inversion techniques. The inference is based on the measurement of the period ratio between the fundamental mode and the first overtone and theoretical results for the period ratio under the hypotheses of coronal density stratification and magnetic field expansion of the wave guide. We present a Bayesian analysis of multiple mode harmonic oscillations for the inversion of the density scale height and magnetic flux tube expansion, under each of the hypotheses. Then, the two models are compared using a Bayesian model comparison scheme to assess how plausible each one is, given our current state of knowledge.
 Temporal Evolution of the Scattering Polarization of the Ca II IR Triplet in Hydrodynamical Models of the Solar Chromosphere — Carlin, E. S.; Asensio Ramos, A.; Trujillo Bueno, J.
Here, we analyze the emergent linear polarization profiles of the Ca II infrared triplet after solving the radiative transfer problem of scattering polarization in time-dependent hydrodynamical models of the solar chromosphere, taking into account the effect of the plasma macroscopic velocity on the atomic level polarization. Our results indicate that the increase of the linear polarization amplitudes caused by macroscopic velocity gradients may be significant in realistic situations. We also study the effect of the integration time, the microturbulent velocity, and the photospheric dynamical conditions, and discuss the feasibility of observing with large-aperture telescopes the temporal variation of the scattering polarization profiles. Finally, we explore the possibility of using a Hanle effect line-ratio technique in the IR triplet of Ca II to facilitate magnetic field diagnostics in dynamic situations.
 Constraining clumpy dusty torus models using optimized filter sets — Asensio Ramos, A.; Ramos Almeida, C.
Recent success in explaining several properties of the dusty torus around the central engine of active galactic nuclei has been gathered with the assumption of clumpiness. The properties of such clumpy dusty tori can be inferred by analysing spectral energy distributions (SEDs), sometimes with scarce sampling given that large aperture telescopes and long integration times are needed to get good spatial resolution and signal. We aim at using the information already present in the data and the assumption of clumpy dusty torus, in particular, the CLUMPY models of Nenkova et al., to evaluate the optimum next observation such that we maximize the constraining power of the new observed photometric point. To this end, we use the existing and barely applied idea of Bayesian adaptive exploration, a mixture of Bayesian inference, prediction and decision theories. We show that Bayesian adaptive exploration can be used to suggest new observations, and ultimately optimal filter sets, to better constrain the parameters of the clumpy dusty torus models. In general, we find that the region between 10 and 200μm produces the largest increase in the expected utility, although sub-mm data from Atacama Large Millimeter Array also prove to be useful. It is important to note that here we are not considering the angular resolution of the data, which is key when constraining torus parameters. Therefore, the expected utilities derived from this methodology must be weighted with the spatial resolution of the data.
 Returning magnetic flux in sunspot penumbrae — Ruiz Cobo, B.; Asensio Ramos, A.
We study the presence of reversed polarity magnetic flux in sunspot penumbra. We applied a new regularized method to deconvolve spectropolarimetric data observed with the spectropolarimeter SP onboard Hinode. The new regularization is based on a principal component decomposition of the Stokes profiles. The resulting Stokes profiles were inverted to infer the magnetic field vector using SIR. We find, for the first time, reversed polarity fields at the border of many bright penumbral filaments in the whole penumbra.
 Six Pyranoside Forms of Free 2-Deoxy-D-ribose — Peña, I.; Cocinero, E. J.; Cabezas, C.; Lesarri, A.; Mata, S.; Écija, P.; Daly, A. M.; Cimas, A.; Bermúdez, C.; Basterretxea, F. J.; Blanco, S.; Fernández, J. A.; López, J. C.; Castaño, F.; Alonso, J. L.
A clear picture of the conformations of isolated 2-deoxy-D-ribose was obtained using chirped pulse and Balle–Flygare Fourier-transform microwave spectrometers, both coupled with laser ablation sources. Two conformers of α-D-deoxyribopyranose and four of β-D-deoxyribopyranose were found on the basis of the spectroscopic rotational parameters and ab initio predictions. The substitution and effective structures of the most abundant conformer have been determined.
 Conformations of D-xylose: the pivotal role of the intramolecular hydrogen-bonding — Peña, I.; Mata, S.; Martín, A.; Cabezas, C.; Daly, A. M.; Alonso, J. L.
Crystalline samples of D-xylose have been vaporized by laser ablation and probed in the gas phase using Fourier transform microwave spectroscopy. The rotational spectrum revealed the existence of two α-D-xylopyranose conformers stabilized by the anomeric effect and cooperative hydrogen bond networks. The experiment spectroscopically tracked fine structural changes upon clockwise and counterclockwise arrangements of the OH groups in the observed conformers. The five monosubstituted 13C species of the most abundant conformer cc-α-4C1 have also been observed in their natural abundance, and its structure has been derived. This work demonstrates the pivotal role that the intramolecular hydrogen-bonding network plays in the conformational behavior of free monosaccharides.
 Accurate molecular structure and spectroscopic properties of nucleobases: a combined computational–microwave investigation of 2-thiouracil as a case study — Puzzarini, C.; Biczysko, M.; Barone, V.; Peña, I.; Cabezas, C.; Alonso, J. L.
 Rotational Spectrum of Paracetamol — Varela, M.; Cabezas, C.; López, J. C.; Alonso, J. L.
In this paper we report the first rotational spectrum of isolated paracetamol. Solid samples of paracetamol were vaporized by laser ablation, expanded in a supersonic jet and characterized by Fourier transform microwave spectroscopy in the 4–10 GHz frequency range. The spectra of a total of four conformers, two with a trans peptidic −CO–NH– functional group arrangement and two with a cis peptidic group arrangement have been observed for the first time. The identification of all the conformers was based on the comparison of the experimental rotational and 14N quadrupole coupling constants with those predicted by ab initio calculations, and relative values of their electrical dipole moment components.
 Probing the γ-Turn in a Short Proline Dipeptide Chain — Cabezas, C.; Varela, M.; Alonso, J. L.
The small peptide derived from proline, N-acetyl-prolinamide (Ac-Pro-NH2), has been investigated using a combination of Fourier transform microwave spectroscopy with laser ablation. Spectral signatures belonging to only one conformer have been detected in the supersonic expansion. Rotational constants and nuclear quadrupole coupling constants of the two 14N nuclei have been used in the characterization of a γ-turn structure in the gas phase, which is stabilized by a CO⋅⋅⋅HN intramolecular hydrogen bond closing a seven-membered ring. A methyl group internal rotation barrier of 354 cm−1 has been determined from the analysis of the A–E splittings.
 Conformational Analysis of Octopamine and Synephrine in the Gas Phase — Cabezas, C.; Simao, A.; Bermúdez, C.; Varela, M.; Peña, I.; Mata, S.; Fausto, R.; Alonso, J. L.
Four and six conformers of the neurotransmitters octopamine and synephrine, respectively, have been identified in the gas phase using a laser ablation device in combination with a molecular-beam Fourier transform microwave spectrometer operating in the 4–10 GHz frequency range. The identification of all of the conformers was based on a comparison of the experimental rotational and 14N quadrupole coupling constants with those predicted by ab initio calculations, as well as the relative values of their electric dipole moment components. The conformational preferences have been rationalized in terms of the various intramolecular forces operating in the different conformers of the studied molecules. All observed species are characterized by an intramolecular hydrogen bond of the type O–H···N established in the side chain of the neurotransmitters, which adopts an extended disposition in their most stable forms. For conformers with a folded side chain, an extra N–H···π hydrogen-bond-type interaction is established between the amino group and the π system of the aromatic ring.
 Conformers of β-aminoisobutyric acid probed by jet-cooled microwave and matrix isolation infrared spectroscopic techniques — Kuş, N.; Sharma, A.; Peña, I.; Bermúdez, M. C.; Cabezas, C.; Alonso, J. L.; Fausto, R.
β-aminoisobutyric acid (BAIBA) has been studied in isolation conditions: in the gas phase and trapped into a cryogenic N2 matrix. A solid sample of the compound was vaporized by laser ablation and investigated through their rotational spectra in a supersonic expansion using two different spectroscopic techniques: broadband chirped pulse Fourier transform microwave spectroscopy and conventional molecular beam Fourier transform microwave spectroscopy. Four conformers with structures of two types could be successfully identified by comparison of the experimental rotational and 14N nuclear quadruple coupling constants with those predicted theoretically: type A, bearing an OH⋯N intramolecular hydrogen bond and its carboxylic group in the trans geometry (H–O–C=O dihedral ∼180°), and type B, having an NH⋯O bond and the cis arrangement of the carboxylic group. These two types of conformers could also be trapped from the gas phase into a cryogenic N2 matrix and probed by Fourier transform infrared (IR) spectroscopy. In situ irradiation of BAIBA isolated in N2 matrix of type B conformers using near-IR radiation tuned at the frequency of the O–H stretching 1st overtone (∼6930 cm−1) of these forms allowed to selectively convert them into type A conformers and into a new type of conformers of higher energy (type D) bearing an NH⋯O=C bond and a O–H “free” trans carboxylic group.
 Observation of dihydrated glycine — Alonso, J. L.; Peña, I.; Sanz, M. E.; Vaquero, V.; Mata, S.; Cabezas, C.; Lopez, J. C.
The complex of glycine with two water molecules glycine–(H2O)2 has been generated by laser ablation in a supersonic expansion and characterised using rotational spectroscopy. The water molecules bind to the carboxylic group of glycine and to each other through three intermolecular hydrogen bonds, closing an eight-membered ring. In the complex, glycine adopts the conformation found to be the most stable for bare glycine.
 Seven Conformers of Neutral Dopamine Revealed in the Gas Phase — Cabezas, C.; Pena, I.; Lopez, J. C.; Alonso, J. L.
The rotational spectrum of neutral dopamine has been investigated for the first time using a combination of Fourier transform microwave spectroscopy with laser ablation. The parameters extracted from the analysis of the spectrum unequivocally identify the existence of seven conformers of dopamine. 14N nuclear quadrupole coupling interactions have been used to determine the orientation of the amino group probing the existence of stabilizing N–H···π interactions for all observed conformers.
 All Five Forms of Cytosine Revealed in the Gas Phase — Alonso, J. L.; Vaquero, V.; Peña, I.; López, J. C.; Mata, S.; Caminati, W.
Herein we have reported the observation of five tauto-meric species of cytosine under isolation conditions in the gas phase and their unequivocal identification by LA-MB-FTMW spectroscopy. The values of the inertial defects show that all species are effectively planar. In the present study of cytosine, we were able to detect keto–imine forms predicted to be more than 1200 cm-1 (in Gibbs values) above the global minimum. 14N nuclear quadrupole patterns make it possible to obtain the spectral signatures for each individual tautomer in the complex sample and thus act as a sort of fingerprint. As an extension of the present study, it would be interesting to investigate how the observed tautomeric behavior is altered by the docking of water molecules to cytosine to create a model environment that would more closely resemble the biological medium.
 Disentangling the Puzzle of Hydrogen Bonding in Vitamin C — Pena, I.; Daly, A. M.; Cabezas, C.; Mata, S.; Bermudez, C.; Nino, A.; Lopez, J. C.; Grabow, J. U.; Alonso, J. L.
Fast-passage Fourier transform microwave spectroscopy in combination with a laser ablation source has been successfully applied to probe vitamin C (L-ascorbic acid) in the gas phase. Its ethyldiol side chain and two hydroxyl groups around the gamma-lactone ring provide five internal rotation axes, enabling vitamin C to assume a wide variety of nonplanar 3D cooperative hydrogen bond networks that can also include the keto and ether functions. The rotational constants extracted from the analysis of the spectrum unequivocally identify the existence of three dominant conformers stabilized by different intramolecular hydrogen bonding motifs forming five-, six-, or seven-membered rings.
 The alanine model dipeptide Ac-Ala-NH2 exists as a mixture of C-7(eq) and C-5 conformers — Cabezas, C.; Varela, M.; Cortijo, V.; Jimenez, A. I.; Pena, I.; Daly, A. M.; Lopez, J. C.; Cativiela, C.; Alonso, J. L.
Microwave spectroscopy has been applied to characterize the conformations adopted in the gas phase by a small peptide derived from alanine, N-acetyl-L-alaninamide (Ac-Ala-NH2). This compound was vaporized by laser ablation and shown to exist as a mixture of Ceq7 and C5 conformers stabilized by a CO—HN intramolecular hydrogen bond closing a seven- or a five-membered ring, respectively. The complicated quadrupole hyperfine structure originated from two 14N nuclei has been completely resolved for both species and the derived nuclear quadrupole coupling constants have been used to determine the Ramachandran angles that describe their molecular shapes.
 Unveiling the Sweet Conformations of d-Fructopyranose — Bermúdez, C.; Pena, I.; Cabezas, C.; Daly, A. M.; Alonso, J. L.
Two conformers of D-fructopyranose are characterized using laser ablation and broadband Fourier-transform microwave spectroscopy. Both species are stabilized by complicated intramolecular hydrogen-bonding networks. Structural motifs related to the sweetness of D-fructopyranose are revealed for the most stable conformer.
 Laboratory and Astronomical Discovery of HydroMagnesium Isocyanide — Cabezas, C; Cernicharo, J.; Alonso, J. L.; Agúndez, M; Mata, S.; Guelin, M.; Peña, I.
We report on the detection of hydromagnesium isocyanide, HMgNC, in the laboratory and in the carbon-rich evolved star IRC+10216. The J = 1-0 and J = 2-1 lines were observed in our microwave laboratory equipment in Valladolid with a spectral accuracy of 3 KHz. The hyperfine structure produced by the nitrogen atom was resolved for both transitions. The derived rotational constants from the laboratory data are B0 = 5481.4333(6) MHz, D0 = 2.90(8) KHz, and eQq(N) = –2.200(2) MHz. The predicted frequencies for the rotational transitions of HMgNC in the millimeter domain have an accuracy of 0.2-0.7 MHz. Four rotational lines of this species, J = 8-7, J = 10-9, J = 12-11, and J = 13-12, have been detected toward IRC+10216. The differences between observed and calculated frequencies are <0.5 MHz. The rotational constants derived from space frequencies are B0 = 5481.49(3) MHz and D0 = 3.2(1) KHz, i.e., identical to the laboratory ones.
 The millimeter wave tunneling–rotational spectrum of phenol — Kolesniková, L.; Daly, A. M.; Alonso, J. L.; Tercero, B.; Cernicharo, J.
The millimeter wave spectra of phenol in the vibrational ground state and the first excited states of the bending and torsion vibrational modes have been studied in the frequency regions of 140–170 GHz and 280–360 GHz. The internal rotation of the hydroxyl group is responsible for the observed tunneling splitting into two substates (vt, vb)+ and (vt, vb)– and more than 3500 distinct tunneling–rotational bR- and bQ-type transitions between them were measured and analyzed. Furthermore, accidental near degeneracies of the (±) and (−) energy levels were observed in case of the ground state and the vb = 1 excited state and the analysis using a two-state effective Hamiltonian including tunneling–rotational Coriolis-like terms was performed. The analysis of the microwave data provided very precise values of the spectroscopic constants necessary for the astrophysical search of phenol. We report a tentative detection for this molecule in the IRAM 30m line survey of Orion KL.
 Laboratory Characterization and Astrophysical Detection of Vibrationally Excited States of Ethyl Cyanide — Daly, A. M.; Bermúdez, C.; López, A.; Tercero, B.; Pearson, J. C.; Marcelino, N.; Alonso, J. L.; Cernicharo, J.
Ethyl cyanide, CH3CH2CN, is an important interstellar molecule with a very dense rotational-vibrational spectrum. On the basis of new laboratory data in the range of 17-605 GHz and ab initio calculations, two new vibrational states, ν12 and ν20, have been detected in molecular clouds of Orion. Laboratory data consist of Stark spectroscopy (17-110 GHz) and frequency-modulated spectrometers (GEM laboratory in Valladolid: 17-170, 270-360 GHz; Toyama: 26-200 GHz; Emory: 200-240 GHz; Ohio State: 258-368 GHz; and JPL: 270-318, 395-605 GHz). More than 700 distinct lines of each species were measured in J up to 71 and in Ka up to 25. The states were fitted with Watson’s S-reduction Hamiltonian. The two new states have been identified in the interstellar medium toward the Orion Nebula (Orion KL). The ground state, the isotopologues of CH3CH2CN, and the vibrationally excited states have been fitted to obtain column densities and to derive vibrational temperatures. All together, ethyl cyanide is responsible for more than 2000 lines in the observed frequency range of 80-280 GHz.
 Full dimensional potential energy surface for the ground state of H+4 system based on triatomic-in-molecules formalism — Sanz-Sanz, C.; Roncero, O.; Paniagua, M.; Aguado, A.
In this work, we present a global potential energy surface for the ground electronic state of the H+4 based on ab initio calculations. The final fit is based on triatomics-in-molecules (TRIM) approximation and it includes extra four-body terms for the better description of some discrepancies found on the TRIM model. The TRIM method itself allows a very accurate description of the asymptotic regions. The global fit uses more than 19,000 multireference configuration interaction ab initio points. The global potential energy surface has an overall root mean square error of 0.013 eV for energies up to 2 eV above the global minimum. This work presents an analysis of the stationary points, reactant and product channels, and crossing between the two lowest TRIM adiabatic states. It is as well included a brief description of the two first excited states of the TRIM matrix, concluding that TRIM method is a very good approximation not only for the ground state but also for at least two of the excited states of H+4 system.
 MULTIMODE calculations of the infrared spectra of H+7 and D+7 using ab initio potential energy and dipole moment surfaces — Qu, C.; Prosmiti, R.; Bowman, J. M.
We present a new ab initio potential energy surface (PES) and a dipole moment surface (DMS) for H+7 in the bound region. The PES is a linear least-squares fit to 42,525 ab initio points whose energies were computed with CCSD(T)-F12b/cc-pVQZ-F12 theory, and the DMS is a fit to dipole moments calculated at MP2 level of theory. The PES and DMS describe the bound region of H+7 precisely. MULTIMODE (MM) calculations of the infrared spectra of H+7 and D+7 were performed using the new PES and DMS. These calculations were carried out at the lowest three stationary points using the single-reference version of MM, and only the five high-frequency modes were considered. The calculated spectra agree well with the recent experimental predissociation action spectra.
 Polarization of molecular angular momentum in the chemical reactions Li + HF and F + HD — Krasilnikov, M. B.; Popov, R. S.; Roncero, O.; De Fazio, D.; Cavalli, S.; Aquilanti, V.; Vasyutinskii, O. S.
 Full-dimensional quantum calculations of the dissociation energy, zero-point, and 10 K properties of H7+/D7+ clusters using an ab initio potential energy surface — Barragán, P.; Pérez de Tudela, R.; Qu, C.; Prosmiti, R.; Bowman, J. M.
Diffusion Monte Carlo (DMC) and path-integral Monte Carlo computations of the vibrational ground state and 10 K equilibrium state properties of the H7+/D7+ cations are presented, using an ab initio full-dimensional potential energy surface. The DMC zero-point energies of dissociated fragments H5+(D5+) + H2(D2) are also calculated and from these results and the electronic dissociation energy, dissociation energies, D0, of 752 ± 15 and 980 ± 14 cm−1 are reported for H7+ and D7+, respectively. Due to the known error in the electronic dissociation energy of the potential surface, these quantities are underestimated by roughly 65 cm−1. These values are rigorously determined for first time, and compared with previous theoretical estimates from electronic structure calculations using standard harmonic analysis, and available experimental measurements. Probability density distributions are also computed for the ground vibrational and 10 K state of H7+ and D7+. These are qualitatively described as a central H3+/D3+ core surrounded by “solvent” H2/D2 molecules that nearly freely rotate.
 Global Potentials for the Interaction between Rare Gases and Graphene-Based Surfaces: An Atom–Bond Pairwise Additive Representation — Bartolomei, M.; Carmona-Novillo, E.; Hernandez, M. I.; Campos-Martinez, J.; Pirani, F.
Global potentials for the physisorption of rare-gas atoms on graphene and graphite, amenable for a variety of dynamics simulations, are reported. An atom–bond pairwise additive form of the potential is used, where the interaction pairs, represented by proper analytical functions, are constituted by the Rg atom (Rg = He, Ne, Ar, Kr) and the C–C bonds of the graphene sheet(s). The parameters of the atom–bond pair potential, derived from the polarizability of the interacting partners, are fine-tuned, exploiting calculations of the prototypical Rg–coronene system using high-level electronic structure methods and large basis sets. The atom–graphene/graphite potential is further expanded in a Fourier series, and it is found that for an accurate representation of the interaction only a small number of corrugation terms need to be added to the laterally averaged potential. The present results compare well with previous data regarding well depths and equilibrium distances at different adsorption sites and, for graphite, the long-range dispersion coefficient C3. In addition, binding energies (eigenvalues of the laterally averaged potentials) are in a fairly good agreement with experimental determinations, providing further support for the reliability of the potentials.
 Quasiclassical Trajectory and Statistical Quantum Calculations for the C + OH -> CO + H Reaction on the First Excited 1(2)A ” Potential Energy Surface — Jorfi, M.; González-Lezana, T.; Zanchet, A.; Honvault, P.; Bussery-Honvault, B.
We report quasiclassical trajectory dynamical calculations for the C(P-3) + OH(X-2 Pi) CO(a(3)Pi) + H(S-2) using a recently developed ab initio potential energy surface for the first electronic state of HCO of 1(2)A ” symmetry. The dependence of integral cross sections on the collision energy was determined. Product energy and angular distributions have also been calculated. Integral cross sections show no energy threshold and decrease as the collision energy increases. The comparison with results obtained from a statistical quantum method seems to confirm that the reaction is mainly dominated by an indirect mechanism in which a long-lived intermediate complex is involved.
 A DFT-based potential energy surface for the H7+ image cluster — Barragán, P.; Prosmiti, R.
 Ortho-H2 and the age of prestellar cores — Pagani, L.; Lesaffre, P.; Jorfi, M.; Honvault, P.; González-Lezana, T.; Faure, A.
We present a simple chemical clock based on the regulation of the deuteration by the abundance of ortho–H2 that slowly decays away from the ortho-para statistical ratio of 3 down to or less than 0.001. We use a chemical network fully coupled to a hydrodynamical model that follows the contraction of a cloud, starting from uniform density, and reaches a density profile typical of a prestellar core. We compute the N2 D+ / 2H+ ratio along the density profile. The disappearance of ortho-H2 is tied to the duration of the contraction and the N2 D+ / 2H+ ratio increases in the wake of the ortho-H2 abundance decrease. By adjusting the time of contraction, we obtain different deuteration profiles that we can compare to the observations. We found that, in all cases, the deuteration profile remains clearly distinguishable whether it comes from the fast collapse or the slow collapse.
 The He + H2+ → HeH+ + H reaction: Ab initio studies of the potential energy surface, benchmark time-independent quantum dynamics in an extended energy range and comparison with experiments — De Fazio, D.; de Castro-Vitores, M.; Aguado, A.; Aquilanti, V.; Cavalli, S.
In this work we critically revise several aspects of previous ab initio quantum chemistry studies of the HeH2+ system. New diatomic curves for the H2+ and HeH+ molecular ions, which provide vibrational frequencies at a near spectroscopic level of accuracy, have been generated to test the quality of the diatomic terms employed in the previous analytical fittings. The reliability of the global potential energy surfaces has also been tested performing benchmark quantum scattering calculations within the time-independent approach in an extended interval of energies. In particular, the total integral cross sections have been calculated in the total collision energy range 0.955–2.400 eV for the scattering of the He atom by the ortho- and para-hydrogen molecular ion. The energy profiles of the total integral cross sections for selected vibro-rotational states of H2+ show a strong rotational enhancement for the lower vibrational states which becomes weaker as the vibrational quantum number increases. Comparison with several available experimental data is presented and discussed.
 H2(v = 0,1) + C+(2 P) → H+CH+ State-to-State Rate Constants for Chemical Pumping Models in Astrophysical Media — Zanchet, A.; Godard, B.; Bulut, N.; Roncero, O.; Halvick, P.; Cernicharo, J.
State-to-state rate constants for the title reaction are calculated using the electronic ground state potential energy surface and an accurate quantum wave-packet method. The calculations are performed for H2 in different rovibrational states, v = 0, 1 and J = 0 and 1. The simulated reaction cross section for v = 0 shows a rather good agreement with the experimental results of Gerlich et al., both with a threshold of 0.36 eV and within the experimental error of 20%. The total reaction rate coefficients simulated for v = 1 are two times smaller than those estimated by Hierl et al. from cross sections measured at different temperatures and neglecting the contribution from v > 1 with an uncertainty factor of two. Thus, part of the disagreement is attributed to the contributions of v > 1. The computed state-to-state rate coefficients are used in our radiative transfer model code applied to the conditions of the Orion Bar photodissociation region, and leads to an increase of the line fluxes of high-J lines of CH+. This result partially explains the discrepancies previously found with measurements and demonstrates that CH+ excitation is mostly driven by chemical pumping.
 Sulfur Chemistry in the Interstellar Medium: The Effect of Vibrational Excitation of H2 in the Reaction S++H2 →SH++H — Zanchet, A.; Agundez, M.; Herrero, V. J.; Aguado, A.; Roncero, O.
Specific rate constants for the S++H2 reaction are calculated using the ground quartet state potential energy surface and quasi-classical trajectories method. The calculations are performed for H2 in different vibrational states v = 0-4 and thermal conditions for rotational and translational energies. The calculations lead to slow rate constants for the H2 vibrational levels v = 0, 1, but a significant enhancement of reactivity is observed when v > 1. The inverse reaction is also studied and rate constants for v = 0 are presented. The calculated rate coefficients are fitted using an improved form of the standard three-parameter Arrhenius-like equation, which is found to be very accurate in fitting rate constants over a wide range of temperatures (10-4000 K). We investigate the impact of the calculated rate coefficients on the formation of SH+ in the photon-dominated region Orion Bar and find an abundance enhancement of nearly three orders of magnitude when the reaction of S+ with vibrationally excited H2 is taken into account. The title reaction is thus one of the principal mechanisms in forming SH+ in interstellar clouds.
 Sensitivity enhancement in high resolution stimulated Raman spectroscopy of gases with hollow-core photonic crystal fibers — Domenech, J. L.; Cueto, M.
We show the first experimental evidence of the sensitivity enhancement that can be achieved in high resolution stimulated Raman spectroscopy of gases using hollow-core photonic crystal fibers (HCPCFs). Using low power cw lasers and a HCPCF containing the gas, we have observed more than four orders of magnitude enhancement of sensitivity when compared with the cw single focus regime, and a similar sensitivity to that achieved in the more sensitive quasi-cw setups with multipass cells.
 Spectroscopic diagnostics of laboratory air plasmas as a benchmark for spectral rotational (gas) temperature determination in TLEs — Parra-Rojas, F. C.; Passas, M.; Carrasco, E.; Luque, A.; Tanarro, I.; Simek, M.; Gordillo-Vazquez, F. J.
We have studied laboratory low pressure (0.1 mbar ≤ p ≤2 mbar) glow air discharges by optical emission spectroscopy to discuss several spectroscopic techniques that could be implemented by field spectrographs, depending on the available spectral resolution, to experimentally quantify the gas temperature associated to transient luminous events (TLEs) occurring at different altitudes including blue jets, giant blue jets, and sprites. we compare available low resolution (3 nm ≤Δλ≤7 nm) N2 1PG field recorded sprite spectra at 53 km (≃1 mbar), and resulting vibrational distribution function, with 1 mbar laboratory glow discharge spectrum (Δλ=2 nm) and synthetic sprite spectra from models. We found that while the relative population of N2(B3Πg,v=2−7) in sprites and laboratory produced air glow plasmas are similar, the N2(B3Πg,v=1) vibrational level in sprites is more efficiently populated (in agreement with model predictions) than in laboratory air glow plasmas at similar pressures.
 Improved determination of the 10-00 rotational frequency of NH3D+ from the high resolution spectrum of the ν4 infrared band — Doménech, J. L.; Cueto, M.; Herrero, V. J.; Tanarro, I.; Tercero, B.; Fuente, A.; Cernicharo, J.
The high resolution spectrum of the ν4 band of NH3D+ has been measured by difference frequency IR laser spectroscopy in a multipass hollow cathode discharge cell. From the set of molecular constants obtained from the analysis of the spectrum, a value of 262817 ± 6 MHz (±3σ) has been derived for the frequency of the 10-00 rotational transition. This value supports the assignment to NH3D+ of lines at 262816.7 MHz recorded in radio astronomy observations in Orion-IRc2 and the cold prestellar core B1-bS.
 Proton transfer chains in cold plasmas of H2 with small amounts of N2. The prevalence of NH4+ — Carrasco, E.; Tanarro, I.; Herrero, V. J.; Cernicharo, J.
The ion–molecule chemistry of the astronomically relevant H3+, N2H+, and NH4+ ions has been investigated in the weakly ionized cold plasmas formed in glow discharges of H2 with small amounts of nitrogen. The concentrations of neutrals and ions were determined by means of mass spectrometry, and electron temperatures and densities were measured using Langmuir probes. A kinetic model was used for the interpretation of the results. It is conjectured that these results can be extrapolated to most of the small molecules predominant in the interstellar medium, which also have proton affinities lower than that of NH3. The results support the predictions of astrochemical models indicating that NH4+ could be a preponderant ion in some warm environments like hot cores, where NH3 molecules have desorbed from the grains.
 Electronic Quenching of OH A 2Σ+ Induced by Collisions with Kr Atoms — Lehman, J. H.; Lester, M. I.; Klos, J.; Alexander, M. H.; Dagdigian, P. J.; Herraez-Aguilar, D.; Aoiz, F. J.; Brouard, M.; Chadwick, H.; Perkins, T.; Seamons, S. A.
Electronic quenching of OH A 2Σ+ by Kr was investigated through experimental studies of the collision cross sections and the OH X 2Π product state distribution. The quenching cross sections decrease with increasing rotational excitation in the excited OH A 2Π electronic state. The OH X 2Π products of quenching exhibit a significant degree of rotational excitation but minimal vibrational excitation. Complementary theoretical studies of the OH (A 2Σ+, X 2Π) + Kr potential energy surfaces (PESs), nonadiabatic coupling, and quasiclassical trajectory calculations were carried out to elucidate the quenching dynamics. Accurate PESs for the two lowest diabatic states of A′ symmetry were computed along with the angularly dependent coupling between them. Coupling in nearly linear HO–Kr configurations provides the mechanism for the observed electronic quenching. A deep attractive well on the OH A 2Σ+ + Kr PES facilitates access to this region of strong coupling. Surface-hopping quasiclassical trajectory calculations yielded quenching cross sections and a OH X 2Π product rotational distribution in good accord with experimental observations.
 The fully quantum state-resolved inelastic scattering of NO(X) plus Ne: experiment and theory — Brouard, M.; Chadwick, H.; Eyles, C. J.; Hornung, B.; Nichols, B.; Scott, J. M.; Aoiz, F. J.; Klos, J.; Stolte, S.; Zhang, X.
Fully Λ-doublet quantum state-resolved differential cross-sections for collisions of NO(X) with neon at a collision energy of 540 cm−1 are presented. Initial state selection of the Ω = 0.5, j = 0.5, f Λ-doublet level of the NO(X) was achieved using hexapole focussing. Both spin-orbit level conserving and spin-orbit level changing transitions have been studied. The experimental results are compared with those obtained from quantum scattering calculations and are shown to be in excellent agreement. Quantum scattering calculations have also been performed on a modified potential energy surface with the attractive region removed, to determine the effects this has on the differential cross-sections. Comparisons are also made with the inelastic scattering of NO(X) with He and Ar.
 Reaction Dynamics and Mechanism of the Cl + HD(v = 1) Reaction: A Quantum Mechanical Study — González-Sanchez, L.; Aldegunde, J.; Jambrina, P. G.; Aoiz, F. J.
 The reactive collision mechanism evinced: stereodynamical control of the elementary Br + H2 -> H + HBr reaction — Herráez-Aguilar, D.; Jambrina, P. G.; Aldegunde, J.; Sáez-Rábanos, V.; de Miranda, M. P.; Aoiz, F. J.
From a kinetics standpoint, reactive molecular collisions are the building blocks of the mechanisms of chemical reactions. In contrast, a dynamics standpoint reveals molecular collisions to have their own internal mechanisms, which are not mere theoretical abstractions: through suitable preparation of the reactants internal and stereochemical states, features of the mechanisms of a reactive molecular collision can be made evident and used as “handles” to control the reaction outcome. Using time-independent quantum dynamical calculations, we demonstrate this for the Br + H2(v = 0-1, j = 2) → H + HBr reaction in the 1.0-1.6 eV range of total energies. Despite its pronounced effect on reactivity, which is in agreement with the predictions from Polanyi rules, reactant vibration is found to have little effect on the mechanism of this endoergic, late-barrier reaction. Analysis of the correlations between directional reaction properties shows that the collision stereochemistry strongly depends on the total energy, but not on how this energy is partitioned between reactant translation and vibration. The stereodynamical preferences implied by the collision mechanisms determine how and to what extent one can control the reaction. Regarding the overall reaction, the extent of control is found to be large near the reaction threshold but not when the total energy is high. Regarding state-to-state reactions, the effect of reactant stereochemistry on the product rotational state distribution is found to be nontrivial and energy dependent.
 A ring polymer molecular dynamics study of the isotopologues of the H + H2 reaction — Suleimanov, Y. V.; de Tudela, R. P.; Jambrina, P. G.; Castillo, J. F.; Saez-Rabanos, V.; Manolopoulos, D. E.; Aoiz, F. J.
The hydrogen exchange reaction and its isotopic variants constitute an excellent benchmark for the assessment of approximate QM methods. In particular, the recently developed ring polymer molecular dynamics (RPMD) technique has been demonstrated to give very good results for bimolecular chemical reactions in the gas phase. In this work, we have performed a detailed RPMD study of the H + H2 reaction and its isotopologues Mu + H2, D + H2 and Heμ + H2, at temperatures ranging from 200 to 1000 K. Thermal rate coefficients and kinetic isotope effects have been computed and compared with exact QM calculations as well as with quasiclassical trajectories and experiment. The agreement with the QM results is good for the heaviest isotopologues, with errors ranging from 15% to 45%, and excellent for Mu + H2, with errors below 15%.
 Rotational alignment effects in NO(X) plus Ar inelastic collisions: A theoretical study — Brouard, M.; Chadwick, H.; Eyles, C. J.; Hornung, B.; Nichols, B.; Aoiz, F. J.; Jambrina, P. G.; Stolte, S.; de Miranda, M. P.
Rotational angular momentum alignment effects in the rotational inelastic scattering of NO(X) with Ar have been investigated by means of close-coupled quantum mechanical, quasi-classical trajectory, and Monte Carlo hard shell scattering calculations. It has been shown that the hard shell nature of the interaction potential at a collision energy of E-coll = 66 meV is primarily responsible for the rotational alignment of the NO(X) molecule after collision. Our study suggests that the rotational alignment and the differential cross sections are sensitive to rather different aspects of the scattering dynamics. The applicability of the kinematic apse model has also been tested and found to be in excellent agreement with exact quantum mechanical scattering theory provided the collision energy is in reasonable excess of the well depth of the NO(X)-Ar potential energy surface.
 Rotational alignment effects in NO(X) plus Ar inelastic collisions: An experimental study — Brouard, M.; Chadwick, H.; Eyles, C. J.; Hornung, B.; Nichols, B.; Aoiz, F. J.; Jambrina, P. G.; Stolte, S.
Rotational angular momentum alignment effects in the rotationally inelastic collisions of NO(X) with Ar have been investigated at a collision energy of 66 meV by means of hexapole electric field initial state selection coupled with velocity-map ion imaging final state detection. The fully quantum state resolved second rank renormalized polarization dependent differential cross sections determined experimentally are reported for a selection of spin-orbit conserving and changing transitions for the first time. The results are compared with the findings of previous theoretical investigations, and in particular with the results of exact quantum mechanical scattering calculations. The agreement between experiment and theory is generally found to be good throughout the entire scattering angle range. The results reveal that the hard shell nature of the interaction potential is predominantly responsible for the rotational alignment of the NO(X) upon collision with Ar.
 Understanding the reaction between muonium atoms and hydrogen molecules: zero point energy, tunnelling, and vibrational adiabaticity — Aldegunde, J.; Jambrina, P. G.; Garcia, E.; Herrero, V. J.; Saez-Rabanos, V.; Aoiz, F. J.
The advent of very precise measurements of rate coefficients in reactions of muonium (Mu), the lightest hydrogen isotope, with H2 in its ground and first vibrational state and of kinetic isotope effects with respect to heavier isotopes has triggered a renewed interests in the field of muonic chemistry. The aim of the present article is to review the most recent results about the dynamics and mechanism of the reaction Mu+H2 to shed light on the importance of quantum effects such as tunnelling, the preservation of the zero point energy, and the vibrational adiabaticity. It has been found that the reaction with H2(v=0) is dominated by the high zero point energy (ZPE) of the products and that tunnelling is largely irrelevant. Accordingly, both QCT calculations that preserve the products’ ZPE as well as those based on the Ring Polymer Molecular Dynamics methodology can reproduce the QM rate coefficients. However, when the hydrogen molecule is vibrationally excited, QCT calculations fail completely in the prediction of the huge vibrational enhancement of the reactivity.
 Chiral Recognition of Amino Acid Enantiomers by a Crown Ether: Chiroptical IR-VCD Response and Computational Study — Avilés-Moreno, J. R.; Quesada-Moreno, M. M.; López-González, J. J.; Martínez-Haya, B.
 Cations in a Molecular Funnel: Vibrational Spectroscopy of Isolated Cyclodextrin Complexes with Alkali Metals — Gamez, F.; Hurtado, P.; Hortal, A. R.; Martinez-Haya, B.; Berden, G.; Oomens, J.
The benchmark inclusion complexes formed by α‐cyclodextrin (αCD) with alkali‐metal cations are investigated under isolated conditions in the gas phase. The relative αCD‐M+ (M=Li+, Na+, K+, Cs+) binding affinities and the structure of the complexes are determined from a combination of mass spectrometry, infrared action spectroscopy and quantum chemical computations. Solvent‐free laser desorption measurements reveal a trend of decreasing stability of the isolated complexes with increasing size of the cation guest. The experimental infrared spectra are qualitatively similar for the complexes with the four cations investigated, and are consistent with the binding of the cation within the primary face of the cyclodextrin, as predicted by the quantum computations (B3LYP/6‐31+G*). The inclusion of the quantum‐chemical cation disrupts the C6 symmetry of the free cyclodextrin to provide the optimum coordination of the cations with the ‒CH2OH groups in C1, C2 or C3 symmetry arrangements that are determined by the size of the cation.
 Harmonic Models in Cartesian and Internal Coordinates to Simulate the Absorption Spectra of Carotenoids at Finite Temperatures — Cerezo, J.; Zuniga, J.; Requena, A.; Ferrer, F. J. A.; Santoro, F.
When large structural displacements take place between the ground state (GS) and excited state (ES) minima of polyatomic molecules, the choice of a proper set of coordinates can be crucial for a reliable simulation of the vibrationally resolved absorption spectrum. In this work, we study two carotenoids that undergo structural displacements from GS to ES minima of different magnitude, from small displacements for violaxanthin to rather large ones for β-carotene isomers. We adopted two approaches to construct the harmonic PES, the Adiabatic (AH) and Vertical Hessian (VH) models and, for AH, two reference coordinate frames: Cartesian and valence internal coordinates. Our results show that when large displacements take place, Cartesian coordinates dramatically fail to describe curvilinear displacements and to account for the Duschinsky matrix, preventing a realistic simulation of the spectra within the AH model, where the GS and ES PESs are quadratically expanded around their own equilibrium geometry.
 Instantaneous normal mode analysis of the vibrational relaxation of the amide I mode of alanine dipeptide in water — Farag, M. H.; Zuñiga, J.; Requena, A.; Bastida, A.
Nonequilibrium Molecular Dynamics (MD) simulations coupled to instantaneous normal modes (INMs) analysis are used to study the vibrational relaxation of the acetyl and amino-end amide I modes of the alanine dipeptide (AlaD) molecule dissolved in water (D2O). The INMs are assigned in terms of the equilibrium normal modes using the Effective Atomic Min-Cost algorithm as adapted to make use of the outputs of standard MD packages, a method which is well suited for the description of flexible molecules. The relaxation energy curves of both amide I modes show multiexponential decays, in good agreement with the experimental findings. It is found that ~85% – 90% of the energy relaxes through intramolecular vibrational redistribution. The main relaxation pathways are also identified. The rate at which energy is transferred into the solvent is similar for the acetyl-end and amino-end amide I modes. The conformational changes occurring during relaxation are investigated, showing that the populations of the alpha and beta region conformers are altered by energy transfer in such a way that it takes 15 ps for the equilibrium conformational populations to be recovered after the initial excitation of the AlaD molecule.
 Conformational changes of beta-carotene and zeaxanthin immersed in a model membrane through atomistic molecular dynamics simulations — Cerezo, J.; Zuniga, J.; Bastida, A.; Requena, A.; Ceron-Carrasco, J. P.
In this work, we investigate systems formed by beta-carotene and zeaxanthin embedded separately in a model lipid bilayer of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) through molecular dynamics (MD) simulations. The study is conducted using an all-atoms model and by analyzing the structural changes that occur at both the carotenoid molecule and the membrane during the simulations. We concentrate specifically on the conformation of the conjugated chain, given the relevance that this feature has in modulating the spectroscopic and antioxidant properties of the carotenoids. A differentiating dynamic behavior of beta-carotene and zeaxanthin within the bilayer is observed in the simulations, which is analyzed in detail through umbrella sampling techniques. This behavior is driven basically by the interactions of the lipid polar heads with the hydroxyl groups of zeaxanthin, which are absent in beta-carotene. These interactions influence the carotenoid orientation, modify the conformational distribution of the dihedral angles of the conjugated chain significantly, and specifically distort the membrane structure.
 Discharge source coupled to a deceleration unit for anion beam generation: Application to H2 – photodetachment — Rudnev, V.; González Ureña, A.
A cathode discharge source coupled to a deceleration unit for anion beam generation is described. The discharge source, made of stainless steel or duralumin electrodes and Macor insulators, is attached to the exit nozzle valve plate at one end, and to an Einzel lens to the other end. Subsequently, a cylindrical retardation unit is attached to the Einzel lens to decelerate the ions in order to optimize the laser beam interaction time required for spectroscopic investigations. The compact device is able to produce beam intensities of the order of 2 × 1012 anions/cm2 s and 20 μrad of angular divergence with kinetic energies ranging from 30 to 120 eV. Using distinct gas mixtures for the supersonic expansion together with a linear time-of-flight spectrometer, anions of great relevance in molecular astrophysics like, for example, H2 −, C3H−, C2 −, C2H−, HCN2 −, CO2 −, CO2H−, C4 −, C4H−, C5H4 −, C5H6 −, C7N−, and C10N− were produced. Finally, in order to demonstrate the capability of the experimental technique the photodetachment cross-section of the metastable H2 −, predominantly in the (v = 0, J = 26) state, was measured following laser excitation at λexc = 565 nm obtaining a value of σph = 0.04 Å2. To the best of our knowledge, it is the first time that this anion cross-section has been measured.
 Decoherence Cross-Section in NO + Ar Collisions: Experimental Results and a Simple Model — Chao, M. S.; Tornero, J.; Lin, K. C.; Stolte, S.; González Ureña, A.
Quantum decoherence can be viewed as the mechanism responsible for the quantum-to-classical transition as the initially prepared quantum state interacts with its environment in an irreversible manner. One of the most common mechanisms responsible for the macroscopically observed decoherence involves collisions of an atom or molecule, initially prepared in a coherent superposition of states, with gas particles. In this work, a coherent superposition of quantum internal states of NO molecules is prepared by the interaction between the molecule with both a static and a radiofrequency electric field. Subsequently, NO + Ar collision decoherence experiments are investigated by measuring the loss of coherence as a function of the number of collisions. Data analysis using a model based on the interaction potential of the collisional partners allowed to unravel the molecular mechanism responsible for the loss of coherence in the prepared NO quantum superposition of internal states. The relevance of the present work relies on several aspects. On the one hand, the use of radio-waves introduces a new way for the production of coherent beams. On the other hand, the employed methodology could be useful in investigating the Stereodynamics of chemical reactions with coherent reagents.

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