Rotationally Inelastic Molecule-Surface Scattering

Abstract

Time-of-flight measurements have been performed on the inelastic scattering of room-temperature beams of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ molecules from a LiF (100) surface. The results show discrete inelastic peaks corresponding to energy losses approximately equal to the molecular rotational excitation energy but shifting with scattering angle. This indicates that rotationally inelastic scattering is dissipative rather than diffractive; i.e., it includes phonon excitations in the solid. The phonons involved can be identified as single Ray-leigh surface phonons.