Dynamics in Neutral DIET from Chemisorbed Molecules

Abstract

Experimental advances since the time of DIET II [1] challenge the theorist to analyze desorption events in quantitative detail. We have chosen to begin such an endeavor by studying the dynamics of neutral DIET. There are several theoretical advantages in studying high-probability neutral, as opposed to low-probability ion, stimulated desorption. While in either case the initial state is often well characterized since the ground state potential energy surface is mapped out by thermal desorption and molecular scattering experiments, only the low-lying excitations are well known from photoemission and inverse- photoemission. Currently the experimental capability exists to look in unprecedented detail at these neutral events. This supplies the theorist with experimentally measured trans translational, vibrational, rotational [2,3] and angular distributions [4] arising from a small number (possibly only one) excited electronic configuration. (Typically one valence excitation is much longer- lived than all others, that is the shallowest excitation of each symmetry providing it is not degenerate with the bulk [5]). In contrast, the low probability events, such as positive ion desorption from metals, may result from a multitude of excitations which are all short-lived, but none of which can be eliminated on the basis of lifetime. Furthermore, the role of minority sites cannot be separated. In this paper we consider in quantitative detail the dynamics of the neutral NO desorption event. Although this is the only system we consider here many of the concepts and methods are general and have already been extended to desorption of physisorbed rare gases [6].