Energy and lifetime of the sigma resonance of oriented O2 physisorbed on Ag(110).

Abstract

We report an experimental and theoretical study of resonance electron scattering by physisorbed ${\mathrm{O}}_{2}$/Ag(110). The cross sections for molecular vibrational excitation, obtained from high-resolution electron-energy-loss spectra, reveal changes in both the energy and the lifetime of the \ensuremath{\sigma} shape resonance of the ${\mathrm{O}}_{2}$ molecule as the coverage is increased from the monolayer to the multilayer regime. With the aid of a layer--Korringa-Kohn-Rostoker calculation of the resonance parameters, which embodies a proper treatment of the unoccupied electronic band structure of the surface, we find that the shift in resonance energy can be attributed to the image potential of the surface, whereas the observed reduction in resonance lifetime in the monolayer is primarily due to the interaction between the molecular resonance state and the unoccupied electronic states of the surface.