Interaction of CO with Cu(111)-Fe

The interaction of CO with a Cu(111) crystal alloyed with different amounts of iron is studied with ellipsometry and AES. Both molecular and dissociative adsorption are observed. The final coverages of oxygen and carbon are equal and such that the sum is the same or larger than the mole fraction of iron in the surface layer. The amount of molecularly adsorbed CO does not increase when a quantity of more than about four monolayers of iron is deposited. This is most probably due to the fact that the iron enrichment of the outer surface layer ceases as well. The isosteric heat of adsorption of CO on the Cu(111)-Fe crystal is 70±15 kJ/mol, independent of coverage and iron content of the surface within experimental error.