Pompage chimique de CH+ et OH+

Presentación con 47 diapositivas; Institut de Planétologie et d'Astrophysique de Grenoble, 3-4 février, 2015The quantum state-to-state cross sections and rate constants obtained for H2+ C+ and H2 + O+ reactive collisions are described together with their implications in astrophysical model of the interstellar mediumPeer Reviewe

Formation of interstellar SH+^+ from vibrationally excited H2_2: Quantum study of S+^+ + H2_2 ⇄\rightleftarrows SH+^+ + H reactions and inelastic collisions

The rate constants for the formation, destruction, and collisional excitation of SH$^+$ are calculated from quantum mechanical approaches using two new SH$_2^+$ potential energy surfaces (PESs) of $^4A''$ and $^2A''$ electronic symmetry. The PESs were developed to describe all adiabatic states correlating to the SH$^+$ ($^3\Sigma^-$) + H($^2S$) channel. The formation of SH$^+$ through the S$^+$ + H$_2$ reaction is endothermic by $\approx$ 9860 K, and requires at least two vibrational quanta on the H$_2$ molecule to yield significant reactivity. Quasi-classical calculations of the total formation rate constant for H$_2$($v=2$) are in very good agreement with the quantum results above 100K. Further quasi-classical calculations are then performed for $v=3$, 4, and 5 to cover all vibrationally excited H$_2$ levels significantly populated in dense photodissociation regions (PDR). The new calculated formation and destruction rate constants are two to six times larger than the previous ones and have been introduced in the Meudon PDR code to simulate the physical and illuminating conditions in the Orion bar prototypical PDR. New astrochemical models based on the new molecular data produce four times larger SH$^+$ column densities, in agreement with those inferred from recent ALMA observations of the Orion bar.Comment: 8 pages, 7 figure

Quantum mechanical calculations of state-to-state cross sections and rate constants for the F + DCl → Cl + DF reaction

9 págs.; 10 figs.; 3 tabs.© 2015 AIP Publishing LLC. We present accurate state-to-state quantum wave packet calculations of integral cross sections and rate constants for the title reaction. Calculations are carried out on the best available ground 12A′ global adiabatic potential energy surface of Deskevich et al. [J. Chem. Phys. 124, 224303 (2006)]. Converged state-to-state reaction cross sections have been calculated for collision energies up to 0.5 eV and different initial rotational and vibrational excitations, DCl(v = 0, j = 0 − 1; v = 1, j = 0). Also, initial-state resolved rate constants of the title reaction have been calculated in a temperature range of 100-400 K. It is found that the initial rotational excitation of the DCl molecule does not enhance reactivity, in contract to the reaction with the isotopologue HCl in which initial rotational excitation produces an important enhancement. These differences between the isotopologue reactions are analyzed in detail and attributed to the presence of resonances for HCl(v = 0, j), absent in the case of DCl(v = 0, j). For vibrational excited DCl(v = 1, j), however, the reaction cross section increases noticeably, what is also explained by another resonance.Financial support from the Scientific and Technological Research Council of TURKEY (TUBITAK) (Project No. TBAG- 112T827) is gratefully acknowledged. Computations have been done on the High Performance and Grid Computing Center (TR-Grid) machine at ULAKBIM/TURKEY. O.R. has been supported by the Ministerio de Economía e Innovación under Grant Nos. CSD2009-00038 and FIS2011-29596-C02 and used the CESGA computing centre under computing ICTS grants and also acknowledge the Chemistry and Molecular Sciences and Technologies COST Action CM1401. J.K. is grateful for the financial support from the U.S. National Science Foundation (Grant No. CHE-1213332 to M. H. Alexander). O.R. and N.B. also acknowledge CSIC for a travelling Grant No. I-LINK0775.Peer Reviewe

Quantum and quasi-classical calculations for the S+ + H2(v,j) → SH+(v′,j′) + H reactive collisions

10 págs; 14 figs.; 2 tabs.State-to-state cross-sections for the S + H(v,j) → SH(v′,j′) + H endothermic reaction are obtained using quantum wave packet (WP) and quasi-classical (QCT) methods for different initial ro-vibrational H(v,j) over a wide range of translation energies. The final state distribution as a function of the initial quantum number is obtained and discussed. Additionally, the effect of the internal excitation of H on the reactivity is carefully studied. It appears that energy transfer among modes is very inefficient that vibrational energy is the most favorable for the reaction, and rotational excitation significantly enhances the reactivity when vibrational energy is sufficient to reach the product. Special attention is also paid to an unusual discrepancy between classical and quantum dynamics for low rotational levels while agreement improves with rotational excitation of H. An interesting resonant behaviour found in WP calculations is also discussed and associated with the existence of roaming classical trajectories that enhance the reactivity of the title reaction. Finally, a comparison with the experimental results of Stowe et al. for S + HD and S + D reactions exhibits a reasonably good agreement with those results.O. R. and N. B. acknowledge CSIC for the travelling grant I-LINK0775. Financial support from the Scientific and Technological Research Council of TURKEY (TUBITAK) (Project No. TBAG- 112T827) and the Ministerio de Economía e Innovación (Spain), for grants CSD2009-00038 and FIS2014-52172-C2, is gratefully acknowledged. The computations have been performed on the High Performance and Grid Computing Center (TR-Grid) at ULAKBIM/TURKEY and CESGA computer center. We also thank the support from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007- 2013)/ERC Grant Agreement no. 610256 (NANOCOSMOS). We also acknowledge the COST action CM1401 ‘Our Astrochemical History’.Peer Reviewe

State-to-state reaction probabilities using bond coordinates: application to the Li+HF(v,j) collision

A time-dependent method to evaluate state-to-state reaction probabilities is presented. For demonstration purposes, the method is applied to Li+HF(v=0, 1, j=0, J=0) reactive collisions using the global potential energy surfaces (GPES). This accuracy of the method is very good when compared with recent time-independent hyperspherical calculations in this system.This work has been supported by DGICYT (Ministerio de Educación y Ciencia, Spain) under Grant Nos. PB97-0027 and PB95-0071, and by the European TMR network Contract No. ERBFMRXCT96-0088. M. L. also thanks the Comunidad Autónoma de Madrid for a Grant. We also want to acknowledge DGICYT and CIEMAT for the use of a CRAY-J90.Peer Reviewe

Electronic and vibrational predissociation in Ari2 photodissociation dynamics

A quantum dynamical study of the ArI2 predissociation where both vibrational and electronic processes can take place was performed. A set of 5 coupled diatomics-in-molecules (DIM) electronic potentials was used. Both perpendicular and linear initial ArI2(X) isomers were considered. Only the a′ state had non-negligible effect on photodissociation dynamics for the linear isomer. Decay rates oscillated as a function of the vibrational excitation of I2(B) but the intramolecular vibrational energy was the main source of energy which occurred in vibrational predissociation.This work has been supported by DGICYT @Ministerio de Educacio´n y Ciencia ~MEC!, Spain# under Grant No. PB95-0071, INTAS under Grant No. 97-31573, and the Spanish–French PICASSO Project No. HF1999-0132. A.A.B. also thanks MEC for sabbatical fellowship.Peer Reviewe

Depolarizing collisions with hydrogen: neutral and singly ionized alkaline earths

Depolarizing collisions are elastic or quasielastic collisions that equalize the populations and destroy the coherence between the magnetic sublevels of atomic levels. In astrophysical plasmas, the main depolarizing collider is neutral hydrogen. We consider depolarizing rates on the lowest levels of neutral and singly ionized alkaly-earths Mg I, Sr I, Ba I, Mg II, Ca II, and Ba II, due to collisions with H. We compute ab initio potential curves of the atom-H system and solve the quantum mechanical dynamics. From the scattering amplitudes we calculate the depolarizing rates for Maxwellian distributions of colliders at temperatures T <10000 K. A comparative analysis of our results and previous calculations in the literature is done. We discuss the effect of these rates on the formation of scattering polarization patterns of resonant lines of alkali-earths in the solar atmosphere, and their effect on Hanle effect diagnostics of solar magnetic fields.Comment: 18 pages, 3 figures. Summitted to ApJ (2014

The lowest triplet state 3A′ of H3 +: Global potential energy surface and vibrational calculations

The adiabatic global potential energy surface of the H3 + system for the lowest triplet excited state of A ' symmetry was computed for an extensive grid of conformations around the minimum region at full configuration interaction ab initia level, using a much more extended basis set than in a previous paper from the same authors. An accurate global fit (rms error lower than 27 cm-1 for energies lower than dissociation into separated atoms and lower than 5 cm-1 for energies lower than the dissociation channel) to these ab initio points and also to part of the previous.calculated points (for a total of 7689 energies in the data set) of the lowest triplet excited state of A′ symmetry is obtained using a diatomics-in-molecules approach corrected by one symmetrized three-body term with a total of 109 linear parameters and 1 nonlinear parameter. This produces an accurate global potential which represents all aspects of the bound triplet excited state of H3 + including the minima and dissociation limits, satisfying the correct symmetry properties of the system. The vibrational eigenstates have been calculated using hyperspherical coordinates with symmetry adapted basis functions with the proper regular behavior at the Eckart singularities. .The accuracy of: the vibrational levels thus obtained is expected to be better than 2 cm-1 with respect to unknown experimental values. Due to the presence of three equivalent minima at collinear geometries (D∝h) the lower vibrational levels are close to triple degenerate. Since the .interconversion barrier between the three minima is about 2640 cm-1, these states split for the upper excited vibrational levels. Such splitting can provide a key feature to identifying the unassigned transitions amongst the many H3 + lines that have been observed in hydrogen plasmas. © 2007 American Institute of Physics.This work has been supported by DGICYT (Ministerio de Educación y Ciencia, Spain) under Grant Nos. PB97-0027 and PB95-0071.Peer Reviewe

Spin-orbit transitions in the N+^+(3PJA^3P_{J_A}) + H2_2 →\rightarrow NH+^+(X2ΠX^2\Pi, 4Σ−^4\Sigma^-)+ H(2S^2S) reaction, using adiabatic and mixed quantum-adiabatic statistical approaches

The cross section and rate constants for the title reaction are calculated for all the spin-orbit states of N$^+$($^3P_{J_A}$) using two statistical approaches, one purely adiabatic and the other one mixing quantum capture for the entrance channel and adiabatic treatment for the products channel. This is made by using a symmetry adapted basis set combining electronic (spin and orbital) and nuclear angular momenta in the reactants channel. To this aim, accurate {\it ab initio} calculations are performed separately for reactants and products. In the reactants channel, the three lowest electronic states (without spin-orbit couplings) have been diabatized, and the spin-orbit couplings have been introduced through a model localizing the spin-orbit interactions in the N$^+$ atom, which yields accurate results as compared to {\it ab initio} calculations including spin-orbit couplings. For the products, eleven purely adiabatic spin-orbit states have been determined with {\it ab initio} calculations. The reactive rate constants thus obtained are in very good agreement with the available experimental data for several ortho-H$_2$ fractions, assuming a thermal initial distribution of spin-orbit states. The rate constants for selected spin-orbit $J_A$ states are obtained, to provide a proper validation of the spin-orbit effects to obtain the experimental rate constants.Comment: 14 pages, 10 figures, submitted to J. Chem. Phy

Communication: theoretical exploration of Au+H2, D2, and HD reactive collisions

The following article appeared in Journal of Chemical Physic 135.9 (2011): 091102 and may be found at http://scitation.aip.org/content/aip/journal/jcp/135/9/10.1063/1.3635772A quasi-classical study of the endoergic Au(1S)+ H2(X1Σg+) → AuHAuH+(2Σ+)+H(2S) reaction, and isotopic variants, is performed to compare with recent experimental results [F. Li, C. S. Hinton, M. Citir, F. Liu, and P. B. Armentrout, J. Chem. Phys. 134, 024310 (2011)]. For this purpose, a new global potential energy surface has been developed based on multi-reference configuration interaction ab initio calculations. The quasi-classical trajectory results show a very good agreement with the experiments, showing the same trends for the different isotopic variants of the hydrogen molecule. It is also found that the total dissociation into three fragments, Au+H+H, is the dominant reaction channel for energies above the H2 dissociation energy. This results from a well in the entrance channel of the potential energy surface, which enhances the probability of H-Au-H insertionA.D.-U. acknowledges a JAE fellowship supported by CSIC. This work is supported by Comunidad Autónoma de Madrid, Grant No. S2009/MAT/1467, and by Ministerio de Ciencia e Innovación, Grant Nos. CSD2009-00038 and FIS2010-18132. The calculations have been performed at CESGA and IFF computing centers. P.B.A. thanks the National Science Foundation for suppor