Stochastic Trajectory Simulations of Gas-Surface Dynamics

Computer simulations of the detailed motion of atoms and molecules interacting with crystal surfaces will be described. Three-dimensional stochastic classical trajectories for the gas atoms and a relatively small number (4-50) of "primary" surface atoms are obtained by numerical integration of generalized Langevin equations of motion. The effects of the remainder of the solid are introduced via a generalized friction which describes dissipation of energy from the primary zone to the rest of the solid, and a fluctuating force which accounts for thermal motion of the solid. Using experimental phonon spectra, friction and fluctuating force items have been constructed which are computationally convenient and which adequately reproduce the motion and response of surface atoms for a variety of materials and crystal faces. Computational results will be presented on angular, velocity, rotational and vibrational scattering distributions, energy accommodation, sticking, thermal desorption, surface diffusion, and vibrational lineshapes and lifetimes.