The electronic structure of the surface methoxy species on Cu{111}

Abstract

Using model calculations for a Cu 25OCH 3 cluster the bonding interaction between the methoxy species and a Cu{111} surface has been investigated. In agreement with recent photoelectron diffraction measurements, OCH 3 is found to adsorb preferentially in the fcc three-fold hollow site with its OC axis perpendicular to the surface. The corresponding vibrational spectrum — measured with high resolution electron energy loss spectroscopy — is compatible with this bonding geometry. Moreover, on the basis of the known structure, selection rules are used to definitively assign the adsorbate-induced features in the photoemission spectrum. There is good agreement between the measured ionisation potentials and those obtained from the model calculations via Koopmans' theorem. Taken together, the results confirm a bonding picture in which charge transfer of metal electrons fills the 2e orbitals of the adsorbed OCH 3 species, leading to a largely ionic bond.