Quantum mechanical investigation on the vibrational relaxation of HF in collisions with H atoms

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Tao, Liang
Alexander, Millard
We investigate the vibrational relaxation of HF(v=2-5) in collisions with H atoms by means of fully-quantum reactive scattering calculations. Our calculations are based on the global ab initio potential energy surface of Stark and Werner which includes, specifically, an accurate description on the reaction barrier and the van der Waals wells in the reactant and product arrangements. We attribute discrepancies between early fluorescence experiments and quasi-classical trajectory calculations to accuracies in the approximate potential energy surface used, in particular inaccuracies in the predicted barrier heights. By suitable linear combinations of the definite parity basis functions, we are able to separate the nominally indistinguishable inelastic relaxation pathways: (1) Inelastic vibrational relaxation unaccompanied by H atom exchange (2) Inelastic vibrational relaxation accompanied by H atom exchange In addition, reactive quenching also contributes to the overall vibrational removal of HF We report state-to-state and overall integral cross sections for each of these channels. The dominant removal process corresponds to vibrational relaxation without H-atom exchange. The magnitude of the vibrational relaxation cross sections are in reasonable overall agreement with the limited experimental data. We also observe sharp structure in the energy dependence of the HF(v=3) removal cross sections. We use an adiabatic-bender analysis to assign this structure to scattering resonances arising from quasi-bound van der Waals states in the HF-H entrance valley.