THE INTERACTION OF CO WITH CU(100)-FE SURFACES

The interaction of CO with Cu(100)-Fe surfaces containing 0-1.7 ML of Fe was studied with ellipsometry and Auger electron spectroscopy. Only reversible molecular adsorption was observed. Dissociation was not ob served at temperatures up to 620 K and pressures up to 0.1 Pa. Apparen tly, fcc Fe(100) surfaces do not dissociate CO under these conditions. Depending on the iron coverage and the pretreatment of the surface, r apid and slow adsorption stages are observed. The rapid adsorption onl y occurs on surfaces that contain iron clusters or are completely cove red with iron, whereas slow adsorption occurs only on surfaces contain ing bare copper. During the slow adsorption stage iron carbonyl-like s pecies are formed, iron clusters are broken up into single iron atoms, or both processes occur together. Since the Cu(100)-Fe surfaces are n ot thermo-stable, it was not possible to determine the heat of adsorpt ion.