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9 pags., 6 figs., Evolved stars are foundries of chemical complexity, gas and dust that provide the building blocks of planets and life, and dust nucleation first occurs in their photosphere. The circumstellar regions enveloping these stars, despite their importance, remain hidden to many observations, and dust formation processes are therefore still poorly understood. Laboratory astrophysics provides complementary routes to unveil these chemical processes, but most experiments rely on combustion or plasma decomposition of molecular precursors under physical conditions far removed from those in space. To reproduce and characterize the bottom-up dust formation process, we have built an ultra-high vacuum machine combining atomic gas aggregation with advanced in situ characterization techniques. We show that carbonaceous dust analogues that formed from low-pressure gas-phase condensation of carbon atoms in a hydrogen atmosphere, in a ratio of carbon to molecular hydrogen similar to that reported for evolved stars, lead to the formation of amorphous carbon nanograins and aliphatic carbon clusters. Aromatic species and fullerenes do not form effectively under these conditions, raising implications for a revision of the chemical mechanisms taking place in circumstellar envelopes., We thank the European Research Council for funding support under Synergy Grant ERC-2013-SyG, G.A. 610256 (NANOCOSMOS). We also acknowledge partial support from the Spanish Research Agency (AEI) through grants MAT2017-85089-c2-1R, FIS2016-77578-R and FIS2016-77726-C3-1-P. Support from the FotoArt-CM Project (P2018/NMT-4367) through the Program of R&D activities between research groups in Technologies 2013, cofinanced by European Structural Funds, is also recognized.

16 pags., 9 figs., 9 tabs. -- Unified Astronomy Thesaurus concepts: Pre-biotic astrochemistry (2079); Astrochemistry (75); Ice destruction (2091); Molecular physics (2058); Molecule destruction (2075); Spectral line identification (2073); Laboratory astrophysics (2004); Theoretical models (2107); Experimental techniques (2078), 2-aminooxazole (2AO), a N-heterocyclic molecule, has been proposed as an intermediate in prebiotic syntheses. It has been demonstrated that it can be synthesized from small molecules such as cyanamide and glycoaldehyde, which are present in interstellar space. The aim of this work is to provide infrared (IR) spectra, in the solid phase for conditions typical of astrophysical environments and to estimate its stability toward UV photons and cosmic rays. IR (4000-600 cm-1) absorption spectra at 20 K, 180 K, and 300 K, IR band strengths, and room-temperature UV (120-250 nm) absorption spectra are given for the first time for this species. Destruction cross sections of ≈9.5 10-18 cm2 and ≈2 10-16 cm2 were found in the irradiation at 20 K of pure 2AO and 2AO:H2O ices with UV (6.3-10.9 eV) photons or 5 keV electrons, respectively. These data were used to estimate half-life times for the molecule in different environments. It is estimated that 2AO could survive UV radiation and cosmic rays in the ice mantles of dense clouds beyond cloud collapse. In contrast, it would be very unstable on the surface of cold solar system bodies like Kuiper Belt objects, but the molecule could still survive within dust grain agglomerates or cometesimals., B.M., V.T., I.T., and V.J.H. are grateful to the Ministerio de Economia y Competitividad (MINECO) of Spain under grant FIS2016-77726-C3-1-P. G.M.M.C., H.C., and C.G.D. acknowledge MINECO support under grant AYA2017–85322-R (AEI/ FEDER, UE), Ph.D. fellowship FPU-17/03172, and MDM2017–0737 Unidad de Excelencia “María de Maeztu”—CAB (CSIC-INTA). I.J.S. acknowledges partial support from the Spanish FEDER (ESP2017-86582-C4-1-R) and the State Research Agency (PID2019-105552RB-C41).

10 pags., 9 figs., 2 tabs., Interstellar (IS) dust analogs, based on amorphous hydrogenated carbon (a-C:H) were generated by plasma deposition in radio frequency discharges of CH4 + He mixtures. The a-C:H samples were characterized by means of secondary electron microscopy, infrared (IR) spectroscopy and UV-visible reflectivity. DFT calculations of structure and IR spectra were also carried out. From the experimental data, atomic compositions were estimated. Both IR and reflectivity measurements led to similar high proportions (≈50%) of H atoms, but there was a significant discrepancy in the sp2/sp3 hybridization ratios of C atoms (sp2/sp3 = 1.5 from IR and 0.25 from reflectivity). Energetic processing of the samples with 5 keV electrons led to a decay of IR aliphatic bands and to a growth of aromatic bands, which is consistent with a dehydrogenation and graphitization of the samples. The decay of the CH aliphatic stretching band at 3.4 μm upon electron irradiation is relatively slow. Estimates based on the absorbed energy and on models of cosmic ray (CR) flux indicate that CR bombardment is not enough to justify the observed disappearance of this band in dense IS clouds., This work was funded by the Spanish MINECO under grants FIS2013-48087-C2-1P and FIS2016-77726-C3-1P. European Union funding under the project ERC-2013-Syg 610256 (NANOCOSMOS) is also acknowledged.

I. Tanarro et al. -- 16 pags., 18 figs., app., We present a proof of concept on the coupling of radio astronomical receivers and spectrometers with chemical reactors and the performances of the resulting setup for spectroscopy and chemical simulations in laboratory astrophysics. Several experiments including cold plasma generation and UV photochemistry were performed in a 40 cm long gas cell placed in the beam path of the Aries 40 m radio telescope receivers operating in the 41–49 GHz frequency range interfaced with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz resolution. The impedance matching of the cell windows has been studied using di erent materials. The choice of the material and its thickness was critical to obtain a sensitivity identical to that of standard radio astronomical observations. Spectroscopic signals arising from very low partial pressures of CH3OH, CH3CH2OH, HCOOH, OCS, CS, SO2 (, The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC-SyG-2013 Grant Agreement No. 610256 NANOCOSMOS and from spanish MINECO CSD2009-00038 (ASTROMOL) under the Consolider-Ingenio Program. We also thank spanish MINECO for funding under grants AYA2012-32032, AYA2016-75066-C2-1-P, FIS2013-48087-C2-1-P, FIS2016-77726-C3-1-P, FIS2016-77578-R, MAT2014- 54231-C4-1-P.

Methyl isocyanate (CH3NCO) was recently found in hot cores and suggested to exist on comet 67P/CG. The incorporation of this molecule into astrochemical networks requires data on its formation and destruction. In this work, ices of pure CH3NCO and of CH3NCO(4%–5%)/H2O mixtures deposited at 20 K were irradiated with a UV D2 lamp (120–400 nm) and bombarded by 5 keV electrons to mimic the secondary electrons produced by cosmic rays (CRs). The destruction of CH3NCO was studied using IR spectroscopy. After processing, the νa–NCO band of CH3NCO disappeared and IR bands corresponding to CO, CO2, OCN−, and HCN/CN− appeared instead. The products of photon and electron processing were very similar. Destruction cross sections and half-life doses were derived from the measurements. Water ice provides a good shield against UV irradiation (half-life dose of ∼64 eV molecule−1 for CH3NCO in water ice), but is not so good against high-energy electrons (half-life dose ∼18 eV molecule−1). It was also found that CH3NCO does not react with H2O over the temperature range 20–200 K. These results indicate that hypothetical CH3NCO in the ices of dense clouds should be stable against UV photons and relatively stable against CRs over the lifetime of a cloud (∼107 yr), and could sublime in the hot core phase. On the surface of a Kuiper Belt object (the original location of comet 67P/CG) the molecule would be swiftly destroyed, by both photons and CRs, but embedded below just 10 μm of water ice, the molecule could survive for ∼109 yr., This work has been funded by the Spanish MINECO under grants FIS2013-48087-C2-1P, FIS2016-C3-1P, and AYA2016- 75066-C2-1-P. J.-C.G. and J.C. also thank the ANR-13-BS05- 0008 IMOLABS and J.-C.G. thanks the Program PCMI (INSU-CNRS) and the Centre National d’Etudes Spatiales (CNES) for funding support. European Union funding under grant ERC-2013-Syg 610256 (NANOCOSMOS) is also acknowledged.

9 pags., 5 figs., 6 tabs., Methyl isocyanate has been recently detected in comet 67P/Churyumov–Gerasimenko (67P/CG) and in the interstellar medium. New physicochemical studies on this species are now necessary as tools for subsequent studies in astrophysics. In this work, infrared spectra of solid CH3NCO have been obtained at temperatures of relevance for astronomical environments. The spectra are dominated by a strong, characteristic multiplet feature at 2350–2250 cm−1, which can be attributed to the asymmetric stretching of the NCO group. A phase transition from amorphous to crystalline methyl isocyanate is observed at ∼90 K. The band strengths for the absorptions of CH3NCO in ice at 20 K have been measured. Deuterated methyl isocyanate is used to help with the spectral assignment. No X-ray structure has been reported for crystalline CH3NCO. Here we advance a tentative theoretical structure, based on density functional theory (DFT) calculations, derived taking the crystal of isocyanic acid as a starting point. A harmonic theoretical spectrum is then calculated for the proposed structure and compared with the experimental data. A mixed ice of H2O and CH3NCO was formed by simultaneous deposition of water and methyl isocyanate at 20 K. The absence of new spectral features indicates that methyl isocyanate and water do not react appreciably at 20 K, but form a stable mixture. The high CH3NCO/H2O ratio reported for comet 67P/CG, and the characteristic structure of the 2350–2250 cm−1 band, makes it a very good candidate for future astronomical searches., This work was funded by the European Union under grant ERC-2013-Syg 610256 (NANOCOSMOS) and by the Spanish MINECO CSD2009-00038 (ASTROMOL) within the Consolider–Ingenio Program. MINECO funding from grants FIS2013-48087-C2-1P, FIS2016-C3-1P, AYA2012- 32032 and AYA2016-75066-C2-1-P is also acknowledged. G. M. acknowledges MINECO PhD grant BES-2014-0693. JCG and JC also thank the ANR-13-BS05-0008 IMOLABS and JCG thanks the Program PCMI (INSU-CNRS) and the Centre National d’Etudes Spatiales (CNES) for funding support

9 págs.; 8 figs.; 3 tabs., Physical and spectroscopic properties of ices of C2H4 and CH4:C2H4 mixtures with 3:1, 1:1 and 1:3 ratios have been investigated at 30 K. Two laboratories are involved in this work. In one of them, the density and refractive index of the samples have been measured by using a cryogenic quartz microbalance and laser interferometric techniques. In the other one, IR spectra have been recorded in the near- and mid-infrared regions, and band shifts with respect to the pure species, band strengths of the main bands, and the optical constants in both regions have been determined. Previous data on ethylene and the mixtures studied here were scarce. For methane, both the wavenumbers and band strengths have been found to follow a regular pattern of decrease with increasing dilution, but no pattern has been detected for ethylene vibrations. The method employed for the preparation of the samples, by vapour deposition under vacuum, is thought to be adequate to mimic the structure of astrophysical ices. Possible astrophysical implications, especially by means of the optical constants reported here, have been discussed. 2016 The Authors; Published by Oxford University Press on behalf of the Royal Astronomical Society, This work has been funded by the Ministerio de Ciencia y Competitividad (MINECO) of Spain under grants FIS2013-48087-C2-1P, FIS2013-48087-C2-2P and AYA2015-71975-REDT ‘Polvo Cosmico’ by the Ministerio de Ciencia e Innovacion of Spain under grant CDS2009-00038 and by the European Research Council project ERC-2013-Syg 610256 ‘Nanocosmos’. GM acknowledges MINECO PhD grant BES-2014-069355.

8 pags., 6 figs., The dynamics of the D + MuH(v = 1) reaction has been investigated using time-independent quantum mechanical calculations. The total reaction cross sections and rate coefficients have been calculated for the two exit channels of the reaction leading, respectively, to DMu + H and DH + Mu. Over the 100-1000 K temperature range investigated the rate coefficients for the DMu + H channel are of the order of 10 cm s and those for the DH + Mu channel vary between 1 × 10 and 8 × 10 cm s. These results point to a virtually barrierless reaction for the DMu + H channel and to the presence of a comparatively small barrier for the DH + Mu channel and are consistent with the profiles of their respective collinear vibrationally adiabatic potentials (VAPs). The effective barrier in the VAP of the DH + Mu channel is located in the reactant valley and, consequently, translation is found to be more efficient than vibration for the promotion of the reaction over a large energy interval in the post threshold region. Below this barrier, the DH + Mu channel can be accessible through an indirect mechanism implying crossing from the DMu + H pathway. The most salient feature found in the present study is revealed in the total reaction cross section for the DMu + H channel, which shows a sharp resonance caused by the presence of a deep well in the vibrationally adiabatic potential. This well has a dynamical origin, reminiscent of that found recently in the vibrationally bonded BrMuBr complex [Fleming, et al., Angew. Chem., Int. Ed., 2014, 53, 1], and is due to the stabilizing effect of the light Mu atom oscillating between the heavier H and D isotopes and to the bond softening associated with vibrational excitation of MuH., This work has been funded by the Spanish Ministry of Science and Innovation under grants CSD2009-00038 and by the MINECO of Spain under grant FIS2013-48087-C2-1P, CTQ2012-37404, CTQ-2015-65033-P. VJH acknowledges also funding from the EU project ERC-2013-Syg 610256. The research was conducted within the Unidad Asociada Química Física Molecular between the UCM and the CSIC of Spain.

26 pags. ; 2 tabs. ; 6 figs., The chemistry of low pressure H2 + O2 discharges with different mixture ratios has been studied in a hollow cathode DC reactor. Neutral and positive ion distributions have been measured by mass spectrometry, and Langmuir probes have been used to provide charge densities and electron temperatures. A simple zero order kinetic model including neutral species and positive and negative ions, which takes into account gas-phase and heterogeneous chemistry, has been used to reproduce the global composition of the plasmas over the whole range of mixtures experimentally studied, and allows for the identification of the main physicochemical mechanisms that may explain the experimental results. To our knowledge, no combined experimental and modelling studies of the heavy species kinetics of low pressure H2 + O2 plasmas including ions has been reported before. As expected, apart from the precursors, H2O is detected in considerable amounts. The model also predicts appreciable concentrations of H and O atoms and the OH radical. The relevance of the metastable species O(1D) and O2(a1Δg) is analysed. Concerning the charged species, positive ion distributions are dominated by H3O+ for a wide range of intermediate mixtures, while H3 + and O2 + are the major ions for the higher and lower H2/O2 ratios, respectively. The mixed ions OH+, H2O+ and HO2 + are also observed in small amounts. Negative ions are shown to have a limited relevance in the global chemistry; their main contribution is the reduction of the electron density available for electron impact processes. © 2015 IOP Publishing, This work has been funded by the MCINN of Spain under grants FIS2010-16455, FIS2013- 48087-C2-1-P and the Consolider Astromol, CDS2009-00038. We thank also the European Research Council for additional support under ERC-2013-Syg 610256-NANOCOSMOS. MJR has received funding from the FPI program of the MCINN, and EC from the JdC program of the same ministry.

19 págs. ; 9 figs. 1 tab., The effect of UV photon (120–200 nm) and electron (2 keV) irradiation of analogues of interstellar carbonaceous dust and of glycine were investigated by means of IR spectroscopy. Films of hydrogenated amorphous carbon (HAC), taken as dust analogues, were found to be stable under UV photon and electron bombardment. High fluences of photons and electrons, of the order of 1019 cm 2 , were needed for a film depletion of a few percent. UV photons were energetically more effective than electrons for depletion and led to a certain dehydrogenation of the HAC samples, whereas electrons led seemingly to a gradual erosion with no appreciable changes in the hydrocarbon structure. The rates of change observed may be relevant over the lifetime of a diffuse cloud, but cannot account for the rapid changes in hydrocarbon IR bands during the evolution of some proto-planetary nebulae. Glycine samples under the same photon and electron fluxes decay at a much faster rate, but tend usually to an equilibrium value different from zero, especially at low temperatures. Reversible reactions re-forming glycine, or the build-up of less transparent products, could explain this behavior. CO2 and methylamine were identified as UV photoproducts. Electron irradiation led to a gradual disappearance of the glycine layers, also with formation of CO2. No other reaction products were clearly identified. The thicker glycine layers (a few hundred nm) were not wholly depleted, but a film of the order of the electron penetration depth (80 nm), was totally destroyed with an electron fluence of 1 1018 cm 2 . A 60 nm ice layer on top of glycine provided only partial shielding from the 2 keV electrons. From an energetic point of view, 2 keV electrons are less efficient than UV photons and, according to literature data, much less efficient than MeV protons for the destruction of glycine. The use of keV electrons to simulate effects of cosmic rays on analogues of interstellar grains should be taken with care, due to the low penetration depths of electrons in many samples of interest., This work was funded by the MCINN of Spain under grants FIS2010-16455 and CDS2009-00038. M. Jiménez-Redondo acknowledges also funding from the FPI program of the MICINN.

6 p. : gráf., The sensitivity of the OD stretching band as a probe to detect HDO in astrophysical ice is discussed based on IR laboratory spectra of HDO molecules embedded in H2O ice. This band is extremely broad and tends to disappear into the absorption continuum of H2O for low-temperature amorphous samples. Detectable HDO/H2O ratios with this technique may range from a few percent for amorphous samples to a few per thousand in crystalline ice. These relatively high upper limits and the appreciable dependence of the band shape on temperature, which would complicate the interpretation of data from many lines of sight, decisively limit the usefulness of the technique for HDO detection in astronomical observations. The process of isotopic H/D exchange in mixed ice of H2O/D2O is also studied through the evolution of the OD band in IR spectra. Isotopic exchange starts at ∼120 K and is greatly accelerated at 150 K, as crystallization proceeds in the ice. Annealed amorphous samples prove to be more favorable for isotope exchange than samples directly formed in crystalline phase. The annealing process seems to favor a polycrystalline ice morphology with a higher defect activity. These morphology differences can be of relevance for deuterium fractionation in astronomical . © 2011 The American Astronomical Society., Funded by the MCINN of Spain under grants FIS2007-61686 and FIS2010-16455; “Ramon y Cajal” program

7 p.: gráf., The so-called hyperquenching technique has been applied to generate water ices containing ammonium and formate ions by sudden freezing of droplets of NH4Cl,NH4COOH, and NaCOOH solutions. Salt deposits were obtained after heating the ices to 210 K to sublimate all water content. All stages are controlled by IR transmission spectroscopy. The NH4 + bands are very much broadened and smeared in the frozen droplets, but stand out strongly when water is eliminated. This fact hints toward the difficulty in ascertaining the presence of this species in astrophysical water-containing ices. Vapor-deposited ices of NH3/HCOOH and H2O/NH3/HCOOH mixtures have also been studied for comparison. HCOO– and NH4 + ions are found to be formed in small proportion even at the lowest temperature, 14 K. By thermal processing, their IR bands become stronger, and at 210 K, after water sublimation, they yield IR spectra similar to those obtained from hyperquenched samples. The observations are interpreted in terms of the varying ion arrangement within the solids along the warming process. A direct comparison to laboratory spectra of irradiated samples, as performed by other groups, is not straightforward. © 2010. The American Astronomical Society, Funding from the Spanish Ministry of Education, Project FIS2007–61686; financial support from CSIC, “JAE-Doc” program; support from Consolider Project “Astromol,” CSD2009–0038.

We report on the detection of a narrow feature at 262816.73 MHz toward Orion and the cold prestellar core B1-bS which we attribute to the 1 0-00 line of the deuterated ammonium ion, NH 3D+. The observations were performed with the IRAM 30 m 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) × 1012 cm-2. Assuming a deuterium enhancement similar to that of NH 2D, we derive N(NH) ≃ 2.6 × 1013 cm -2, i.e., an abundance for ammonium of a few 10-11. © 2013. The American Astronomical Society. All rights reserved., MICINN for funding support through grants, AYA2009-07304, CSD2009-00038, Fis2010-16455 and Fis2012-38175.French national PCMI program.

Ammonia ice has been detected on different astrophysical media ranging from interstellar medium (ISM) particles to the surface of various icy bodies of our solar system, where nitrogen is also present. We have carried out a detailed study of amorphous NH3 ice and NH3:N2 ice mixtures, based on infrared (IR) spectra in the mid-IR (MIR) and near-IR (NIR) regions, supported by theoretical quantum chemical calculations. Spectra of varying ice thicknesses were obtained and optical constants were calculated for amorphous NH3 at 15 K and 30 K and for a NH3:N2 mixture at 15 K over a 500-7000 cm-1 spectral range. These spectra have improved accuracy over previous data, where available. Moreover, we also obtained absolute values for the band strengths of the more prominent IR features in both spectral regions. Our results indicate that the estimated NH3 concentration in ISM ices should be scaled upward by 30%. © 2013. The American Astronomical Society. All rights reserved.

The Astrophysical Journal 146.5 (2013): 125, reproduced by permission of the AAS, 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 H 2 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. For comparison, we also recompile previous results of state-to-state rate constants of the C ++H2 for H2 in rovibrational state v, j = (0,0), (1,0), (1,1), and (2,0). 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, This work has been supported by the program CONSOLIDER-INGENIO 2010 of the Ministerio de Ciencia e Innovación under grant CSD2009-00038, entitled “Molecular Astrophysics: the Herschel and Alma era,” by grants No. FIS2011-29596-C02 and FIS2010-16455, and by Comunidad Autónoma de Madrid (CAM) under grant No. S-2009/MAT/ 1467.

15 páginas; 5 figuras; PACS:52.57.Kk Fast ignition of compressed fusion fuels.- 52.80.Hc Glow; corona.- 52.70.Kz Optical (ultraviolet, visible, infrared) measurements., Time-resolved emission spectroscopy and quadrupole mass spectrometry are used for the experimental diagnostics of a low pressure (8 Pa) modulated dc hollow cathode discharge of H2 + 10% N2. The time-dependent experimental results are reasonably accounted for by a zero-order kinetic model developed in our group and checked previously with steady-state measurements (Carrasco et al 2011 Phys. Chem. Chem. Phys. 13 19561), which is now validated under more stringent conditions. In addition to the discharge precursors, which are partly recycled in wall reactions, NH3 is produced in small but appreciable amounts. The slower evolution of NH3, as compared with H2 and N2, is traced back to the multistep surface reaction mechanism responsible for its production. An analysis of the time variation of optical emission measurements shows that excited NH(c 1Π) radicals are essentially formed in the electron-impact dissociation of NH3., This work has been funded by the MICINN of Spain under projects FIS2010-16455 and CSD2009-00038. EC acknowledges also funding from the JdC program of the MICINN.

An extensive set of experimental measurements on the dynamics of the H + + D 2 and D + + H 2 ion-molecule reactions is compared with the results of quantum mechanical (QM), quasiclassical trajectory (QCT), and statistical quasiclassical trajectory (SQCT) calculations. The dynamical observables considered include specific rate coefficients as a function of the translational energy, E T, thermal rate coefficients in the 100-500 K temperature range. In addition, kinetic energy spectra (KES) of the D + ions reactively scattered in H + + D 2 collisions are also presented for translational energies between 0.4 eV and 2.0 eV. For the two reactions, the best global agreement between experiment and theory over the whole energy range corresponds to the QCT calculations using a Gaussian binning (GB) procedure, which gives more weight to trajectories whose product vibrational action is closer to the actual integer QM values. The QM calculations also perform well, although somewhat worse over the more limited range of translational energies where they are available (E T < 0.6 eV and E T < 0.2 eV for the H + + D 2 and D + + H 2 reactions, respectively). The worst agreement is obtained with the SQCT method, which is only adequate for low translational energies. The comparison between theory and experiment also suggests that the most reliable rate coefficient measurements are those obtained with the merged beams technique. It is worth noting that none of the theoretical approaches can account satisfactorily for the experimental specific rate coefficients of H + + D 2 for E T ≤ 0.2 eV although there is a considerable scatter in the existing measurements. On the whole, the best agreement with the experimental laboratory KES is obtained with the simulations carried out using the state resolved differential cross sections (DCSs) calculated with the QCT-GB method, which seems to account for most of the observed features. In contrast, the simulations with the SQCT data predict kinetic energy spectra (KES) considerably cooler than those experimentally determined. © Royal Society of Chemistry, Funding by the Spanish Ministry of Science and Innovation (MCINN) (grants CTQ2008-02578, FIS2010-16455 and CSD2009-00038). FPU fellowship AP2006-03740. The research was conducted within the Unidad Asociada Dpto. Química Física I (UCM–CSIC). The Computational resources used for the DRW code calculations in this work were provided by the University of Queensland (Centre for Computational Molecular Science) and the Australian Research Council (LIEF grant LE0882357: ‘A Computational Facility for Multiscale Modelling in Computational Bio and Nanotechnology’).

19 páginas, 4 figuras, 3 tablas., An experimental diagnosis and kinetic modeling of the ionic chemistry in low pressure DC plasmas of H2/Ar has been carried out. The studies were performed at pressures of 2 Pa and 0.7 Pa, in a hollow-cathode discharge reactor, using as plasma precursor a H2/Ar mixture with 15% Ar content. Experimental measurements include distributions of ion fluxes to the cathode, as well as electronic temperatures and densities in the plasma glow. Besides the species resulting directly from electron impact ionization (H+, H2+, Ar+ and Ar2+), the ions H3+ and ArH+ were found to be formed in large amounts through protonation reactions in the glow. In spite of the not too large variation in the pressure of the two plasmas, the differences in the ion distributions are worth mentioning. In the 2 Pa discharge (but not in the 0.7 Pa), H3+ was the dominant ion and ArH+ exceeded markedly the Ar+ signal. On the other hand, the appearance of Ar2+ in the two plasmas points at the relevance of high energy electrons. The experimental results can be accounted for by a simple kinetic model, after including corrections for the presence of a small fraction (< 3%) of high energy (> 50 V) electrons and for the attenuation of the Ar+ ions in the sheath through asymmetric charge exchange with H2., This work has been funded by Ministry of Education of Spain under grants ENE2006-14577-C04-C03, FIS2007-61686.

Ice mixtures of methane and water are investigated by means of IR spectroscopy in the 14-60 K range. The spectroscopic research is focused on the symmetry-forbidden ν1 band of CH4 and the dangling bond bands of water. The ν1 band is visible in the spectra of the mixtures, revealing a distorted methane structure which co-exists with the normal crystalline methane. The water dangling bond bands are found to increase their intensity and appear at red-shifted frequency when distorted methane is present. Methane adsorbed on water micropores or trapped inside the amorphous solid water structure is assumed to be responsible for these effects. CH 4 mobility in water ice depends on the deposition method used to prepare the samples and on the temperature. After warming the samples to 60 K, above the methane sublimation point, a fraction of CH4 is retained in the water ice. An adsorption isotherm analysis is performed yielding the estimation of the desorption energy of CH4 on H2O amorphous surfaces. © 2010 the Owner Societies., Funding from the Spanish Ministry of Education, Project FIS2007-61686. financial support from CSIC, ‘‘JAE-Doc’’ program.

This article presents a quasiclassical trajectory method for the calculation of cumulative reaction probabilities by sampling of the helicity quantum number of the reagents (k). The method is applied to the D + H 2 reaction at various total angular momentum (J) values, and the helicity-resolved quasiclassical cumulative reaction probabilities are compared to their quantum mechanical counterparts. The agreement between the two sets of results is fairly good. In particular, k-dependent, J-independent reaction thresholds found with quantum methods are reproduced by the quasiclassical calculations. The shift of these thresholds with increasing k, which has been previously attributed to the quantum bottleneck states taking part in the reaction, is revisited and discussed also in terms of the reaction stereodynamics. © Royal Society of Chemistry, Financed by the DGES of Spain under grants CTQ2005-08493-C01-01, FTN2003-0828-C03-03 and FIS 2004-00456. The research was performed within the Unidad Asociada ‘‘Química Física Molecular’’ between the Universidad Complutense and CSIC.

This paper describes crossed beam experiments and quasiclassical trajectory (QCT) calculations for the 'insertion' reaction O(1D)+D2 at a collision energy (Ec=25.9 kJ mol-1) much higher than the calculated barrier (∼8.4 kJ mol-1) for the competitive 'abstraction' mechanism, which takes place along the excited state potential energy surfaces (PES). Adiabatic QCT calculations were carried out on the ground 11A' and first excited 11A'' PESs developed by Dobbyn and Knowles. Non-adiabatic contributions from the excited 21A' PES to the reaction were considered by means of a trajectory surface hopping method. QCT calculations were also performed at Ec=22.2 kJ mol-1 to compare with previous experimental results. Excellent agreement was found between experiment and QCT predictions at Ec=22.2 kJ mol-1, while at the higher Ec of 25.9 kJ mol-1 only a qualitative agreement was noted. In all cases, the comparison was significantly improved with respect to QCT calculations on a previous version of the ground state PES.

A theoretical study of the dynamics of the O(1D) + D2 reaction has been performed at the collision energies (Ec¼ 86.7 meV and 138.8 meV) of a recent high resolution molecular beam experiment using the D-atom Rydberg ‘‘ tagging’’ technique (X. Liu et al., Phys. Rev. Lett., 2001, 86, 408). The theoretical calculations havebeen carried out on the ab initio 11A0, 11A00 and 21A0potential energy surfaces (PES) by Dobbyn and Knowles.The quasiclassical trajectory (QCT) method was used for the investigation on the ground electronic PES (11A0).Non-adiabatic transitions between this PES and the excited 21 A0 were considered by using a trajectory surface hopping methodology. An accurate quantum mechanical (QM) approach was used for the reaction on the excited 11A0PES. The theoretical results are globally in good agreement with the measurements and indicate that, although the excited 11A00 surface does contribute to the reaction at the higher collision energy, a large part of the observed increase in backward reactive scattering is due to the reaction over the ground state 11 A0PES., Financial support by the Spanish Ministry of Science and Technology through the program ‘‘Ramón y Cajal’’. Financial support from the ‘‘Plan Andaluz de Investigación’’(group FQM-205). This work has been financed by the DGES of Spain under contracts PB98-0762-C03 and REN-2000-1557-CL1, and by the EU Research Training Network ‘‘Reaction Dynamics’’ HPRN-CT-1999-00007. The facilities providedby the Centro de Supercomputación Complutense (SG Origin 2000)

A simple experimental setup for the production of cold samples for spectroscopy is described. The samples are deposited under vacuum on a cold metallic surface whose temperature is controlled between 80 and 323 K by varying the heat flow balance between a liquid nitrogen reservoir and a power transistor. Tests of temperature stability and thermal inertia, as well as a set of reflection–absorption infrared and thermal desorption spectra, are reported as a demonstration of the performance of the system. © 2002 American Institute of Physics., MCT of Spain under Grant No. REN 2000-1557 CLI.

The well-known radical and ion scavenger techniques of application in amorphous hydrogenated carbon film deposition studies are investigated in relation to the mechanism of tritium and deuterium co-deposition in carbon-dominated fusion devices. A particularly successful scheme results from the injection of nitrogen into methane/hydrogen plasmas for conditions close to those prevailing in the divertor region of present fusion devices. A complete suppression of the a-C: H film deposition has been achieved for N2/CH4 ratios close to one in methane (5%)/hydrogen DC plasma. The implications of these findings in the tritium retention control in future fusion reactors are addressed.© 2002 IOP Publishing Ltd, Supported by Dirección General de Investigación Científica y Técnica (DGICYT) under Project FTN2000-0915-C03. MECD of Spain, under Project SB2000-0051.

Quasiclassical trajectory reactive scattering and quantum mechanical calculations were performed for the O(1D)+H2 (v = 0,j = 0) reaction on the Dobbyn-Knowles ab inito potential energy surfaces (PES). The reaction was investigated using high resolution Rydberg-atom 'tagging' time-of-flight technique. Results indicated that the detailed experimental measurements with rovibrational state resolution at 56 meV collision energy could be explained by resorting to adiabatic calculations on the ground 1 1A′ PES. © 2002 American Institute of Physics, Support from the ‘‘Plan Andaluz de Investigación group FQM-205. support by the Spanish Ministry of Science and Technology through the program ‘‘Ramon y Cajal.’’ The quantum mechanical scattering calculations on the 1 1 A8 surface have been performed on a NEC SX5 vector supercomputer through a grant of the Institut du Développement des Resources en Informatique Scientifique ~IDRIS, in Orsay, France. This work has been financed in part by the DGES of Spain under Contract Nos. PB98-0762 and REN-2000-1557-CL1 and by the EU Research Training Network ‘‘Reaction Dynamics’’ HPRN-CT-1999-00007.

Several applications of time resolved infrared (IR) absorption spectroscopy with different spectral resolutions and time scales were described for the modeling and diagnostic of cold plasmas produced in square wave modulated hollow cathode discharges. An efficient and sensitive way to test the relevance of the different individual mechanisms was revealed by these methods in comparison with the usual plasma diagnostic methods of the stationary state. The temporal hierarchy of the characteristic dynamical features involved in the global kinetics of the plasma was analyzed by the modulation of the discharge at different frequencies and time-resolved diagnostics at different time scales.© 2002 Elsevier Science, Financial support:the SEUID of Spain (Projects PB98-0762-C03-02, PB96-0881) and the Consejería de Educación y Cultura, C.A.M. (Project 07N/0024/1999)

22 pags.; 4 figs., The rotational relaxation of nitrogen molecules in collisions with neon has been studied in supersonic expansions. N2 rotational temperatures have been determined from resonance-enhanced-multiphoton-ionization (REMPI) spectra performed in a series of supersonic molecular beams of N2 diluted in Ne. Terminal flow velocities and translational temperatures for the two expansion partners have been obtained from mass-selected time-of-flight measurements. From the measured data, the approximate isentropic behavior of the expansion could be verified and the thermal cross section for N2/Ne rotational relaxation at very low temperatures could be derived. The cross section increases from a value of ≈35 Å2 at 5 K, goes through a maximum of about 55 Å2 between 10 and 20 K, and then decreases smoothly to ≈25 Å2 for T = 60 K. The relaxation cross section for N2/Ne collisions is larger than that for N2/N2 collisions below roughly 20 K and smaller above this temperature. © 2001 American Chemical Society, Financed by the MEC of Spain under Project PB98-0762-C03.

The rotational relaxation of molecular nitrogen has been investigated down to temperatures of about 5 K with a combination of resonance-enhanced multiphoton ionization and supersonic beam time-of-flight techniques. The average rotational relaxation cross section obtained shows a maximum value of 50-60 A2 at 20-30 K. For lower temperatures this cross section decreases and reaches a value smaller than 30 A2 at T ≈ 5 K. For temperatures above 30 K, the cross section decreases slowly as the temperature grows and converges approximately to the determinations from other non-jet techniques and theoretical estimates available for T > 80 K. The results are compared to previous measurements from other groups using different methods, and general good agreement is found. However, we observe a significant discrepancy with some of the data from electron-beam-induced fluorescence that yield much larger cross sections for temperatures lower than 30 K.© 1999 American Chemical Society, Program “Incorporación a Espan˜a de Doctores y Tecnólogos”of the Spanish Ministerio de Educación y Ciencia (MEC) and from the program “Ayuda a la Investigación” of the Fundación Caja de Madrid. Grants from the FPI program of the MEC. This work was financed by the MEC of Spain under DGICYT Project PB95/0918-C03.

6 pags.; 4 figs., An experimental setup for the production of pulsed supersonic He beams to be used for plasma edge diagnosis in fusion devices is described. A compromise between compact design, low cost, and good quality of the probe beams has been met. The main characteristics of the generated beams, such as pulse shape, absolute flux intensity, and velocity distribution, differ in general from those expected for ideal beam performance and have been determined and optimized experimentally. A first test of this He beam source at the TJ-I UP Torsatron in Madrid is also reported. © 1997 American Institute of Physics, T.D.-R. acknowledges the financial support through a F.P.I. fellowship of the Ministry of Education of Spain. This work was partially financed by the DGICYT of Spain under Grant No. PB94-0128.

The dynamics of the F+HD reaction has been studied by means of quasiclassical trajectory calculations on an ab initio potential energy surface (PES) at several collision energies. At the collision energy of 85.9 meV and for the DF+H isotopic channel of the reaction, there is a remarkable agreement between calculated and experimental results, in both the center of mass (c.m.) differential cross sections (DCS) and in the simulation of the laboratory (LAB) time of flight (TOF) and angular distributions (AD). The good agreement also extends to the lower collision energy of 58.6 meV for this channel of the reaction. In contrast, the simulation of the LAB angular distributions for the HF+D channel shows strong discrepancies between theory and experiment at both collision energies, which can be traced back to the absence of a forward peak in the calculated cm. DCS for HF(v′=3). Simulations made from QCT calculations on other PES with important HF(v′=3) forward scattering contributions also fail to reproduce the overall AD. The theoretical findings and especially the roles of translational energy and initial rotational momentum on the dynamics of this reaction are discussed in terms of the topology of the PES through the analysis of individual trajectories. © 1995 American Institute of Physics., Financed by theDGICYT of Spain ~PB92-0219-C03. German–Spanish Scientific Exchange Program ‘‘Acciones Integradas’’ HA-074, HA-113. Funded by the Deutsche Forschungsgemeinschaft as part of the SFB 216. The ab initio calculations were performed on the CRAY-YMP of the Höchstleistungsrechenzentrum Jülich. support by the German Fonds der Chemischen Industrie.

Differential and total state-to-state cross sections for the D + H2 (v=0, j=0-3) → HD (v′, j′) + H reaction in the 0.35-1.10 eV collision energy range, have been calculated on the LSTH surface using the QCT method. The results are commented on and compared to recent quantum mechanical calculations and to experimental measurements. © 1990 Published by Elsevier B.V., Financed in part by the CICYT of Spain under Grant PB 870263.