Quasiclassical trajectory calculations of photodissociation of Ar–H2O(X̃–Ã) and H2O(X̃–Ã)

Abstract

We present results of full-dimensional quasiclassical trajectory calculations of the photodissociation of H2O(3νOH,X̃–Ã) and Ar–H2O(3νOH,X̃–Ã) at 243 and 218 nm, and compare the resulting OH rotational distributions, and also relate them to recent experiments of Nesbitt and co-workers [D. F. Plusquellic, O. Votava, and D. J. Nesbitt, J. Chem. Phys. 101, 6356 (1994)]. The dynamics calculations make use of a new six degree-of-freedom potential for Ar–H2O(Ã), which is reported here. The potential is based on a previously reported ab initio H2O Ã-state potential, a semiempirical Ar–OH(2Π) potential, and a semiempirical Ar–H potential, together with an appropriate switching function to ensure permutation symmetry with respect to the two H atoms. Initial conditions for the trajectories are obtained from a product of a Husimi phase-space density for the Ar–H2O(X̃) intermolecular modes and a Wigner/classical phase-space density for the H2O(X̃) intramolecular modes. The Husimi phase-space density is derived from the ground-state wave function for Ar–H2O(X̃), using a previous spectroscopically empirical potential. To assess the accuracy of the trajectory approach, trajectory calculations are also reported for X̃–Ã photodissociation of H2O in the ground vibrational state at 166 nm and compared with the corresponding full-dimensional quantum wave packet calculations of von Dirke and Schinke. To further assess the accuracy of the Ã-state potential surface for H2O, calculations for H2O(4νOH,X̃–Ã) are also reported at 218 nm and compared with experiment. Rotation/vibration distributions of the OH fragment are also calculated for photodissociation of Ar–H2O(4νOH,X̃–Ã) at 218 nm.