Vibrational excitation in molecule–surface collisions. Analytic modeling vs classical trajectories

Abstract

The problem of translational to vibrational energy redistribution occurring in collisions between diatomic molecules and solid surfaces is considered. Attention is focused solely on a mechanism which is a consequence of a molecule–surface interaction giving rise to an intramolecular potential whose equilibrium separation is a function of distance from the surface. This ‘‘three-body’’ chemical effect is totally unrelated to mechanical excitation due to spring compression. While past work has emphasized the specific process of charge transfer/harpooning as a means for obtaining such an interaction, the mechanism is more general in the sense that it depends only upon the topology of the potential energy surface (PES) and not on what electronic properties gave rise to the topology. The T to V energy redistribution is treated both within the context of analytical models over necessarily simplified PES as well as numerically evaluated classical trajectories over more complex and realistic ones. Systematic studies are presented in which the relationship between energy conversion and PES characteristics are established. Conditions under which the analytic models provide reasonable representations of the collision are noted. I2 is the molecule of choice in this work.