Angle-resolved and variable impact energy electron vibrational excitation spectroscopy of molecules adsorbed on surfaces

Discrete energy losses occur when a beam of low energy electrons (30 eV) is scattered from surfaces. For a gas–solid interface, inelastic scattering can occur through excitation of molecular vibrations. Chemical identification, molecular structures and bonding sites can be inferred from the energies of the characteristic losses. The angle and impact energy dependence of the mode intensity can give additional information which in many cases further elucidates the bonding. A consistent picture of the vibrational excitation mechanisms is derived which leads to the identification of helpful selection rules. Discussion will center on the simplest chemical adsorbate of H on W(100) and Ni(111). The application of the basic ideas to diatomic and polyatomic adsorbates will be mentioned briefly.