COMBINED CLASSICAL TRAJECTORY AND QUANTUM SCATTERING ANALYSIS OF COLLISION-INDUCED VIBRATIONAL-ENERGY TRANSFER - DEACTIVATION OF HCL(V=1) IN AN AR GAS

A simple method for calculating vibrational transition probabilities i n three-dimensional atom-diatomic collisions, which we call the classi cal approach quantum encounter (CAQE) method, is presented. It consist s of using suitably initiated classical trajectories as a means of gen erating ensembles of phase-space points corresponding to the hard part of collisions in which the repulsive core of the interaction potentia l is sampled; these are then used as input to standard expressions for computing quantum vibrational transition probabilities. The method is applied to study the temperature dependence of the vibrational deacti vation of HCl(v = 1) in collisions with Ar atoms. It can be generalize d, however, to treat vibrational energy exchange in encounters between two polyatomic molecules. Strengths and weaknesses of the method are discussed and comparisons are made with a preceding simpler theory whe rein the classical dynamics of the approach was replaced by statistica l approximations.