Vibrational Excitations of Methane Monolayer Physisorbed on Ag(111) Surfaces

Abstract
Vibrational spectra of a CH4 monolayer were studied by high-resolution electron energy loss spectroscopy. Monolayer of CH4 was physisorbed on a Ag(111) surface at 40 K. The dependence of vibrational excitation cross section on the incident electron energy and scattering geometry was studied. Excitation of the v 4 mode was mainly excited by dipole scattering, while the v 2 mode was excited via impact scattering. The combinational mode was observed at the incident electron energies of 6-10 eV. The effect of negative-ion resonance is discussed from the experimental results.