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* 2S1 (excitation energy E*=20.6 eV) and 2S3 (E*=19.8 eV) atoms were measured. The operation of the Penning mechanism, viz., He*+AHe+A++e, 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.