Inelastic scattering of electrons by absorbate vibrations in the impact scattering regime: CO on Ni(100) as an example

We have used a formalism developed by us recently to carry out a series of calculations of electron-energy-loss (EELS) cross sections for excitations of vibrations in a c(2×2) overlayer of CO on the Ni(100) surface. The calculations explore impact scattering and cover a wide range of energies and scattering geometries. We examine the sensitivity of the various cross sections to the CO bond length, and also to the C-Ni distance. We also find a series of selection rules that apply to the impact-scattering problem. These are discussed and illustrated with numerical calculations of the angular variation of the EELS cross sections.