0000000000466026
AUTHOR
Alexandre Faure
Intermolecular potential and rovibrational states of the H2O–D2 complex
International audience; A five-dimensional intermolecular potential for H2O-D-2 was obtained from the full nine-dimensional ab initio potential surface of Valiron et al. [P. Valiron, M. Wernli, A. Faure, L. Wiesenfeld, C. Rist, S. Kedzuch, J. Noga, J. Chem. Phys. 129 (2008) 134306] by averaging over the ground state vibrational wave functions of H2O and D-2. On this five-dimensional potential with a well depth D-e of 232.12 cm (1) we calculated the bound rovibrational levels of H2O-D-2 for total angular momentum J = 0-3. The method used to compute the rovibrational levels is similar to a scattering approach-it involves a basis of coupled free rotor wave functions for the hindered internal r…
Communication: Rotational excitation of interstellar heavy water by hydrogen molecules
Cross sections and rate coefficients for low lying rotational transitions in D(2)O induced by para-H(2) collisions are presented for the first time. Calculations have been performed at the close-coupling level with the deuterated variant of the H(2)O-H(2) interaction potential of Valiron et al. [J. Chem. Phys. 129, 134306 (2008)]. Rate coefficients are presented for temperatures between 1 and 30 K and are compared to the corresponding rate coefficients for H(2)O. Significant differences caused by the isotopic substitution are observed and are attributed to both kinematics and intramolecular geometry effects. Astrophysical implications are briefly discussed in view of the very recent detecti…
The 2014 KIDA network for interstellar chemistry
Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011.
Ortho−ParaH2Conversion by Proton Exchange at Low Temperature: An Accurate Quantum Mechanical Study
We report extensive, accurate fully quantum, time-independent calculations of cross sections at low collision energies, and rate coefficients at low temperatures for the ${\mathrm{H}}^{+}+{\mathrm{H}}_{2}(v=0,j)\ensuremath{\rightarrow}{\mathrm{H}}^{+}+{\mathrm{H}}_{2}(v=0,{j}^{\ensuremath{'}})$ reaction. Different transitions are considered, especially the ortho-para conversion ($j=1\ensuremath{\rightarrow}{j}^{\ensuremath{'}}=0$) which is of key importance in astrophysics. This conversion process appears to be very efficient and dominant at low temperature, with a rate coefficient of $4.15\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\ma…
H-2, H-3(+) and the age of molecular clouds and prestellar cores
Measuring the age of molecular clouds and prestellar cores is a difficult task that has not yet been successfully accomplished although the information is of paramount importance to help in understanding and discriminating between different formation scenarios. Most chemical clocks suffer from unknown initial conditions and are therefore difficult to use. We propose a new approach based on a subset of deuterium chemistry that takes place in the gas phase and for which initial conditions are relatively well known. It relies primarily on the conversion of H 3 + into H 2D + to initiate deuterium enrichment of the molecular gas. This conversion is controlled by the ortho/para ratio of H2 that i…
Rotational quenching of monodeuterated water by hydrogen molecules
Cross sections and rate coefficients for low lying rotational transitions in HDO induced by para and ortho-H(2) collisions are presented for the first time. Calculations have been performed at the close-coupling and coupled-states levels with the deuterated variant of the H(2)O-H(2) interaction potential of Valiron et al. [J. Chem. Phys., 2008, 129, 134306]. Rate coefficients are presented for temperatures between 5 and 100 K and are compared to the corresponding rates for H(2)O and D(2)O. Significant differences caused by the isotopic substitution, in particular the C(2v) symmetry breaking, are observed. Finally, our rates are found to be significantly larger (by up to three orders of magn…
Quantum mechanical study of the proton exchange in the ortho-para H2 conversion reaction at low temperature
Ortho-para H2 conversion reactions mediated by the exchange of a H+ proton have been investigated at very low energy for the first time by means of a time independent quantum mechanical (TIQM) approach. State-to-state probabilities and cross sections for H+ + H 2 (v = 0, j = 0,1) processes have been calculated for a collision energy, Ec, ranging between 10-6 eV and 0.1 eV. Differential cross sections (DCSs) for H+ + H2 (v = 0, j = 1) → H+ + H2 (v′ = 0, j′ = 0) for very low energies only start to develop a proper global minimum around the sideways scattering direction ( ≈ 90°) at Ec = 10-3 eV. Rate coefficients, a crucial information required for astrophysical models, are provided between 10…