Dynamics of gas-surface interactions: Thermal desorption of Ar and Xe from platinum

Three-dimensional stochastic classical trajectory studies have been carried out of the thermal desorption of isolated Ar and Xe atoms from the (111) face of platinum. Realistic interaction potentials that produce quantitative agreement with experimental sticking probabilities and angular and velocity scattering distributions were employed. Energy exchange with lattice phonons was included accurately via empirically chosen friction and fluctuating forces. Application of techniques for the simulation of “infrequent events” allowed studies to be extended to experimentally accessible lifetimes. Atoms were found to desorb preferentially to wide angles, with mean energy considerably lower than 2k times the surface temperature. Significant curvature of the Arrhenius plots was exhibited, and pre-exponential factors were found to be lower than characteristic frequencies. These effects were determined to be mainly dynamical in origin; i.e., they cannot be described by conventional transition-state-theory models.