Formation and dynamics of hot-precursor hydrogen atoms on metal surfaces: Trajectory simulations and stochastic models

The results of a theoretical study of H atoms colliding with a Cu(111) surface are presented. The metal is treated as a five-layer slab of 150 atoms, and all dynamics are classical. The formation of trapped “hot-precursor” atoms on the surface is examined, as well as the nature of their motion on the surface and their energy and momentum dissipation. Connections are made with recent Eley–Rideal experiments, for which hot-atom precursors may play an important role. To facilitate future simulations of Eley–Rideal and hot-atom reactions on metals, simple stochastic models are developed to describe hot-atom energy dissipation. A Fokker–Planck equation is used to model the hot-atom energy distribution. Quasi-Langevin terms, which simulate fluctuation and dissipation consistent with this Fokker–Planck description, are developed for the hot-atom equations of motion. These quasi-Langevin terms are different from the hydrodynamic forms used for Brownian-type motion.