PERTURBATION OF THE ADSORBATE ELECTRONIC-STRUCTURE BY LOCAL-FIELDS AT SURFACE-DEFECTS

PAX (photoemission of adsorbed xenon) measurements provide direct evidence for rather strong localized surface potential variations near surface step sites. In the present study the influence of the associated localized electric fields parallel to the surface on the electronic structure of nearby adsorbed CO molecules is examined within a simple theoretical model: a point charge in the vicinity of a Cu5CO cluster. The results demonstrate a downwards shift and a splitting of the CO2-pi* derived cluster orbital leading to an increased CO2-pi* occupation as a contribution to C-O bond weaking near step defects.