Rare-Gas Scattering from LiF: Correlation with Lattice Properties. II

Abstract

The scattering of thermal energy atomic beams of Ne, Ar, Kr, and Xe from the (001) face of LiF has been studied. Two dominant peaks in the scattering distributions in the plane of incidence are observed: one peak remains fixed with respect to the crystal whereas the position of the other displays a strong dependence on angle of incidence, incident energy, and azimuthal orientation of the target. The former peak is associated with the normal modes of the lattice, in particular with dipole–induced dipole attractive forces produced by longitudinal optical modes in next‐nearest‐neighbor unlike ion directions. The latter peak is discussed in terms of the surface properties of the crystal, e.g., interaction potential and elastic properties, the latter acting on the transfer of tangential momentum. For Ne, additional peaks occur which arise from diffraction effects. The present results provide additional insight into the phenomenon of preferential scattering reported earlier and strongly emphasize the inadequacies of existing theoretical descriptions of thermal energy atomic and molecular (TEAM) scattering from surfaces, especially when applied to the surfaces of ionic crystals.