Penning-Ionization Electron Spectroscopy of Chemisorbed CO

Abstract

Energy distributions of electrons ejected from clean and CO-covered Pd(111) surfaces by impact with metastable He* $2^{1}S$ (excitation energy ${E}^{*}=20.6$ eV) and $2^{3}S$ (${E}^{*}=19.8$ eV) atoms were measured. The operation of the Penning mechanism, viz., ${\mathrm{He}}^{*}+A\ensuremath{\rightarrow}\mathrm{He}+{A}^{+}+{e}^{\ensuremath{-}}$, is demonstrated for adsorbed CO whose valence orbitals could be identified. Thereby a new surface spectroscopic technique with extreme sensitivity to the outmost atomic layer is established.