The bonding of simple carboxylic acids on Cu(110)

We present a study of the bonding of formate (HCOO) and acetate (CH3COO) ch emisorbed on Cu(110) using core level spectroscopies in combination with th eoretical calculations. For the first time, we apply x-ray emission spectro scopy (XES) to these systems. When XES is used in conjunction with x-ray ab sorption spectroscopy (XAS) and ab initio calculations, new information abo ut the electronic interaction in the adsorbate-substrate system is provided . In particular, we have used the azimuthal orientation of the COO-surface bond on the (110) surface, to make a complete partition into x, y, and z or bital contributions. The surface bond is found to be predominantly ionic. F or the case of adsorbed formate, the covalent bonding is dominated by 6a(1) /7a(1), (sigma)-type, frontier orbitals, interacting with the Cu valence ba nd. The resulting hybrid orbitals form a distribution of states that cross the Fermi level. The contribution from adsorbate pi-type orbitals is small. The chemical bond formation of adsorbed acetate is very similar to that of formate. In addition, states with metal character have been identified for the outermost CH3-group of acetate. These are delocalized states of mainly local sigma-character. The spectral features due to states of local pi-cha racter in the adsorbed acetate are well described within the framework of h yperconjugation. (C) 2000 American Institute of Physics. [S0021-9606(00)003 18-4].