Interactional effects between adsorbates on metal single-crystals

Abstract

The interactions between CO species chemisorbed on Ni (111) and the interactions between CO and S on S-poisoned Ni (111) have been studied by using infrared reflection-absorption spectroscopy. For CO chemisorption on the clean surface, evidence for long-range chemical interactions is presented in which donor-acceptor effects prevail in determining CO hybridization states. For CO chemisorption on S-poisoned Ni (111) , evidence for the influence of local electrostatic effects in the vicinity of the S atom is presented. Slightly longer range S....CO interactions also occur, removing the CO chemisorption ability of next-neighbour Ni sites to S. These two interaction mechanisms extend over about six Ni atom neighbours to S. Surface Penning ionization electron spectroscopy has been used to probe the filled molecular orbitals of chemisorbed CO on Ni (111) , and direct evidence for the involvement in chemisorption of the CO 2n* orbitals is found, both on the clean N i(111) surface and on K + Ni (111).