Coadsorbate Interactions: Sulfur and CO on Ni(100).
CORNELL UNIV ITHACA NY LAB OF ATOMIC AND SOLID STATE PHYSICS
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The influence of a S adlayer on CO adsorption onto Ni100 is examined. Tight binding extended Huckel calculations on a three layer model slab indicate that the interabsorbate separation distance determines not only the mechanism, but also the effect of the interaction. If the C-S distance is short, sulfur induces site blockage of CO chemisorption by means of a direct, repulsive interadsorbate mechanism. If the separation is increased beyond the normal S-C bond range, the sulfur adatoms work indirectly via modification of the electronic structure of the substrate. This is a form of through-bond coupling. It is consistent with the well-documented sulfur poisoning of CO adsorption and its usual explanation via relative electronegativities of adsorbates, but there are some conceptual differences. At longer coadsorbate separations, there is an interesting reversal of the bonding trends, which has some experimental support.
- Inorganic Chemistry