Surface optical excitations associated with CO chemisorption on Ni(111)

Surface optical excitations associated with CO chemisorption on Ni(111) have been studied using surface reflectance spectroscopy (SRS) and electron-energy-loss spectroscopy (ELS). SRS measurements using s- and p-polarized light in the photon energy range 4-35 eV are analyzed using a simple dielectric model to deduce surface optical transitions. A comparison of the SRS and ELS results for CO-Ni(111) with the optical excitations in gas- and solid-phase CO and in transition-metal carbonyls reveals correlations in spectral structure which are used as a basis to suggest possible identifications of the surface optical transitions; these include charge-transfer excitations from the metal to the CO (2*) affinity level at 6 eV, singlet valence transitions X+1A 1(52*) of the chemisorbed CO molecule near 8 eV, and Rydberg excitations of the CO orbitals near 13 eV and above. © 1978 The American Physical Society.