Classical diffusion model of vibrational predissociation of van der Waals complexes Part III. Comparison with quantum calculations

Abstract

The quantum and classical expressions for the vibrational predissociation rates of two-degree-of-freedom triatomic van der Waals complexes are compared. The classical rate is approximated by its diffusional counterparts (Parts I and II of this series), while the expression for the quantum rate is based on the generalization of the Landau method (E. E. Nikitin and L. Pitaevski, Phys. Rev. A, 1994, 49, 695). The ratio of the classical to quantum rates is expressed by an analytical formula which shows the reason for the difference between the classical and quantum rates and which explains a similar trend of both rates with the change of the key parameters of the vibrational predissociation event. We conclude that the occasional numerical closeness of classical and quantum rates results from the delicate interplay between the classical diffusion through a narrow energy layer and quantum tunneling through the broad energy range.