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

The dissociative classical dynamics of a model van der Weals (vdW) complex studied by running long-time trajectories is compared with the diffusion ap proximation. The latter describes the chaotic motion, which corresponds to the intramolecular vibrational redistribution (IVR) and the vibrational pre dissociation (VP), by the Fokker-Planck equation. The energy diffusion coef ficient in the Fokker-Planck equation is calculated from the short-time dyn amics relevant to one oscillation of the vdW bond. The numerical and analyt ical results of this study combined with the truncated mean first passage t ime description of the diffusional decay (Part I of this series) yield a si mple analytical expression for the classical VP rate constant that identifi es key parameters which determine the VP rate.