Inelastic Scattering of Atoms and Molecules from Solid Surfaces

Abstract

In this paper some recent developments in the field of atomic and molecular inelastic scattering from surfaces are highlighted. At the low energies involved (20meV to 2eV) the incident particles probe the topmost surface layer in a nondestructive manner. Inelastic scattering of light particles (e.g. He atoms) is dominated by single phonon excitation or annihilation and thus provides a probe of surface vibrational structure or other accessible energy loss channels. High resolution time of flight techniques coupled with supersonic beam sources provide measurements of surface phonon dispersion relations out to the zone edge. The scattering of heavier atoms and molecules is more complicated. Multiphonon processes and excitations of molecular internal states are involved. Both time of flight and state specific detection techniques must be applied to get a full picture of molecular inelastic scattering. This is illustrated by studies of rotational energy transfer in the scattering of NO from Ag(111). Coupling of translational to rotational motion is found to be a dominant energy transfer channel while vibrational excitation has a very small probability. Measured rotational state distributions exhibit several interesting features including rotational rainbows and rotational alignment. Quantum mechanical calculations on a simple model of the scattering provide a semi-quantitative description of the results and allow information on the interaction potentials to be derived. © 1983 IOP Publishing Ltd.