Multiple-quantum excitation probabilities of Einstein-like modes of surfaceadsorbates induced by He-atom scattering

Abstract

Experimental data exhibiting multiple-quantum excitation ofthe vibrational modes of decoupled, oscillating adsorbates on asurface via impact by a He atom are reviewed for the cases ofcarbon monoxide and heavy rare gases adsorbed on metalsubstrates. The experimental scattering spectra are analysedusing a dynamical scattering model that predicts correctly theangular dependences of the distributions of multiphonon excitations and the variation with incident energy and adsorbatefrequency. The agreement between experiment and theoryindicates that the details of the He-surface interactionpotential are relatively unimportant for incident energies muchhigher than the vibrational energy. The model is used to predictthe excitation probabilities of other possible vibrational modeswhich have not yet been observed using helium-atom scattering.