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Abstract:
Experimental data exhibiting multiple-quantum excitation of the vibrational modes of decoupled, oscillating adsorbates on a surface via impact by a He atom are reviewed for the cases of carbon monoxide and heavy rare gases adsorbed on metal substrates. The experimental scattering spectra are analysed using a dynamical scattering model that predicts correctly the angular dependences of the distributions of multiphonon excitations and the variation with incident energy and adsorbate frequency. The agreement between experiment and theory indicates that the details of the He-surface interaction potential are relatively unimportant for incident energies much higher than the vibrational energy. The model is used to predict the excitation probabilities of other possible vibrational modes which have not yet been observed using helium-atom scattering.
