A theoretical investigation of microscopic dynamics and time scales of predesorption processes

Abstract

When an internal mode of an absorbate is excited with enough energy to break the absorbate–surface bond, the adsorbate may desorb in a manner similar to predissociation (or unimolecular reaction) in isolated molecules. In this article, we set up a simple, microscopic model for this ‘‘predesorption’’ process and investigate the influence of various aspects of the model on the time scale of predesorption. These comparisons include quantum mechanical vs classical treatment, and the inclusion vs neglect of surface vibrations. For this simple analog of a ‘‘unimolecular reaction,’’ we find that classical mechanics predicts shorter lifetimes; and that the effect of surface vibrations is far less pronounced in quantum mechanics.