Theoretical studies of vibrational excitation in collisions of O( ³P) with H₂O(1A1)

The quasiclassical trajectory method is used to calculate cross sections for vibrational excitation in O(³P)+H₂O(000) collisions. The potential surface is a Sorbie-Murrell fit to the ab initio MBPT calculation of Bartlett and Purvis. State-to-state transition probabilities are evaluated using the histogram method to discretize the H₂O good action variables obtained from a classical perturbative treatment of the molecular Hamilton-Jacobi equation. Integral cross sections are presented for all one-quantum excitations [(010), (100), and (001)] plus some multiquantum excitations. Rotational distributions for each final vibrational state indicate that significant rotational excitation accompanies vibrational excitation. The angular distributions for vibrationally excited final states indicate sidewards peaking. The resulting (001) cross section is in reasonable agreement with experimental shock tube results. The analogous (010) excitation cross section is larger than the corresponding experimental value. Although the experimental error is large, at least part of the difference between theory and experiment is associated with a small time dependence in the computed actions for this very floppy mode.