A perturbation–trajectory method for the study of gas–surface collision dynamics

Abstract

A perturbation–trajectory method for determining the dynamics of gas–surface collision processes is described. The method is based upon the assumption that the motions of Q-zone atoms are unaffected by the collision process at the lattice surface. This assumption leads to a P-zone Hamiltonian that incorporates the effects of Q-zone motion in terms of time-varying P-zone–Q-zone interactions. The collision dynamics of the P zone are determined from an ensemble of stoichastic trajectories using this coupled Hamiltonian. The method is applied to three systems: (1) collinear inelastic atomic collisions with a ten-atom chain, (2) the inelastic scattering and absorption of NO on a Ag(111) surface, and (3) the collision and subsequent surface reactions of SiH2 on a Si(111) surface. Comparison of the perturbation results with those obtained using the full system Hamiltonian shows that under certain conditions the perturbation procedure yields very accurate results with a significant reduction in computational requirements. In general, the accuracy of the perturbation calculations increases as the incident-to-lattice-atom mass ratio decreases. A decrease in the strength of the interaction between the incident molecule and the Q zone, the incident translational energy, or the lattice temperature also improves the accuracy of the perturbation treatment. The method is therefore best suited to the study of inelastic, light-molecule collisions with heavy-atom surfaces at low temperature. Comparisons with previously reported gas–surface studies that employ a Langevin approximation are also given.