Resonant Auger studies of CO adsorbed on two groups ofdtransition metals

Resonant Auger measurements for CO adsorbed on six different d-metal surfaces—Ni(100), Pd(100), Pt(111), Cu(100), Ag(110), and Au(110)—have been performed at the C 1s and O 1s x-ray-absorption maxima. Peaks appearing at the high-kinetic-energy side of the spectra are identified and interpreted as being due to decay processes involving occupied 2${\mathrm{\pi }}^{\mathrm{*}}$-metal d orbitals (2${\mathrm{\pi }}_{\mathit{o}}$). These features provide valuable information on the adsorbate-substrate interaction, and a qualitative understanding of their behavior was obtained based on the properties of the core excited intermediate states. A feature close to the Fermi level in the photoelectron spectrum was found to resonate around the C 1s edge for the CO/Ag(110) system. This effect was interpreted as resonant photoemission of the 2${\mathrm{\pi }}^{\mathrm{*}}$-derived hybrid orbitals. A feature is observed in the C 1s excited decay spectrum for CO/Ni(100), that is interpreted as the result of a shake up in the resonant Auger decay. Differences in the relative intensities of the resonant Auger peaks due to different adsorption sites are discussed, with the CO/H/Ni(100) system as a model. Photon-energy-dependent resonant Auger results for CO/Ni(100) c(2×2) are presented. The degree of localization of the excited electron, and its influence on the decay spectra is discussed.