Generalized Langevin theory for gas-solid processes: Continuum elastic treatment of surface lattice dynamics

Model studies of the systematics of elementary atom-solid energy exchange processes are presented. The studies are based on the generalized Langevin equation (GLE) classical trajectory method [S. A. Adelman and J. D. Doll, J. Chem. Phys. 64, 2375 (1976)] and on a full isotropic continuum elastic treatment of both bulk and surface solid atom velocity response functions χ(t). Within both bulk (BEM) and surface (SEM) elastic models, the solid dynamics is parameterized by two bulk properties, a Debye frequency ωD and a transverse to longitudinal sound velocity ratio Rs. The Debye model used in earlier GLE simulations is a specialization of the BEM, R s=1.0, and thus does not include surface effects, e. g., Rayleigh waves, accounted for in the SEM. The main results of the trajectory studies are as follows: Gas-solid energy transfer efficiency within the BEM depends very sensitively on Rs (for fixed ωD). For physical Rs values <0.2-0.6, BEM energy transfer is often much larger than Debye energy transfer. SEM energy transfer is relatively insensitive to R s and is, moreover, dominated by the Rayleigh mode contribution to χ(t). The SEM energy transfer is often fortuitously of comparable magnitude to Debye energy transfer.