Precursor Dynamics

Stochastic classical trajectory simulations have been carried out of the adsorption and desorption of intact CO molecules on nickel surfaces. The study employed a sequence of gas-surface potential energy hypersurfaces that are essentially the same in the vicinity of the chemisorption minimum, but which differ in the region of approach to the minimum. Potentials exhibiting a single minimum (no precursor) and double minimum (intrinsic precursor) with various angular dependences, depths and barrier heights have been investigated. Rates of trapping into, thermalization, diffusion and escape from precursors have been calculated. The influence of precursor wells on the angular, velocity, rotational energy and temperature dependence of sticking, and on the partitioning of energy in desorbed molecules has been studied. Proposed experimental signatures of precursors will be discussed.