Classical diffusion model of vibrational predissociation of van der Waals complexes. Part II. Comparison with trajectory calculations and analytical approximations

Abstract

The dissociative classical dynamics of a model van der Waals (vdW) complex studied by running long-time trajectories is compared with the diffusion approximation. The latter describes the chaotic motion, which corresponds to the intramolecular vibrational redistribution (IVR) and the vibrational predissociation (VP), by the Fokker–Planck equation. The energy diffusion coefficient in the Fokker–Planck equation is calculated from the short-time dynamics relevant to one oscillation of the vdW bond. The numerical and analytical results of this study combined with the truncated mean first passage time description of the diffusional decay (Part I of this series) yield a simple analytical expression for the classical VP rate constant that identifies key parameters which determine the VP rate.