Inelastic gas-surface scattering

Helium and molecular hydrogen scattering from copper is calculated to examine general features of scattering for these systems, especially the quantum mechanics of the scattering process, both for the motion of the particle and the excitations of the lattice. This thesis outlines the nature of the scattering problem, develops techniques for calculating scattering probabilities, develops an approximation for the potential, and calculates scattering probabilities. The quantum mechanics of the system is essential both for the particle because of diffraction, discrete rotational transitions, and selective adsorption and for the lattice because the occupation of only a few phonon modes changes during the scattering. In many ways it is similar to neutron scattering from solids except the scattering is much stronger so that its theoretical treatment, while similar to the Born approximation used for neutron scattering, uses distorted waves instead of plane waves. Using a formal method of thermally averaging the scattering probabilities of self-consistent one-phonon approximation is developed to study the effect of inelastic scattering on diffraction and selective adsorption resonances. The relationship of this scheme to the distorted wave Born approximation is shown on a diagrammatic expansion of the distorted wave Born series