A useful picture of chemisorption on metal surfaces is one in which a localized molecule is formed between the adatom and its nearest neighbor substrate atoms. The interaction responsible for the molecule formation is treated as the coupling between the adsorbate state and a group orbital formed from a linear combination of atomic orbitals on the substrate atoms. Within the surface molecule picture, level width and level shift functions, given by Newns modification of the Anderson theory, have been calculated and the resulting adatom density of states function has been obtained. This has been done for model systems in which the substrate is either a free electron metal or a tightbinding p-band metal and the adsorbate is s or p like. The results show how it is possible to simultaneously have narrow virtual levels due to chemisorption (~ 1 eV) which previously implied weak interactions and also high binding energies ( 3 eV) as are observed experimentally.
Citation: Surface Science
Pub Type: Journals