Discrete-continuum hybrid model for gas-surface collisions. I. Trajectories with single, multiple collisions and capture

This paper presents a model and calculations for the scattering of atomic and molecular beams from solid surfaces. In this model, the solid is represented as an elastic continuum for the energy exchange processes and phonon propagation while the paniculate nature of the projectile as well as the corrugation due to the discreteness of the solid lattice are retained. This hybrid continuum/discrete representation of the solid is a suitable description for relaxation dynamics of adsorbates on surfaces and low energy collisions of gas particles with surfaces. The projectile-surface interaction is described in terms of compliance coefficients which are effective spring and damping constants for the solid. This makes the handling of the solid extremely practical. The full set of compliance coefficients for all possible surface forces and moments are given. As applications, trajectory calculations are presented using the parameters of the He + LiF system as well as models with deeper wells and softer solids. Although with the parameters of the He + LiF system only single collisions and elastic wave excitation are observed, the model calculations display additional interesting phenomena such as multiple collisions, resonances and capture of the projectile.