Lateral Hopping of CO on Ag(110) by Multiple Overtone Excitation

A novel type of action spectrum representing multiple overtone excitations of the upsilon(M-C) mode was observed for lateral hopping of a CO molecule on Ag(110) induced by inelastically tunneled electrons from the tip of a scanning tunneling microscope. The yield of CO hopping shows sharp increases at 261 +/- 4 mV, corresponding to the C-O internal stretching mode, and at 61 +/- 2, 90 +/- 2, and 148 +/- 7 mV, even in the absence of corresponding fundamental vibrational modes. The mechanism of lateral CO hopping on Ag (110) was explained by the multistep excitation of overtone modes of upsilon(M-C) based on the numerical fitting of the action spectra, the nonlinear dependence of the hopping rate on the tunneling current, and the hopping barrier obtained from thermal diffusion experiments.ope

Inelastic photoemission due to scattering by surface adsorbate vibrations

By measuring the very low energy photoemission spectra of the CO/Cu(001) surface with a high resolution, we have found the energy loss components due to inelastic scattering of electrons near the Fermi level by the CO vibrational modes. The main energy loss structure appears as a step at 254 meV below the Fermi edge for ^C^O. An isotope shift of the step to 240 meV was observed when ^C^O was adsorbed. This observation confirms that this step arises from the energy loss of photoelectrons near the Fermi level through the excitation of the C-O stretching mode