The interaction of 0, with a Cu(lll)-Ni alloy and the reaction of sorbed oxygen with H, has been investigated with ellipsometry and AES. The surface alloys were prepared by dissociation of nickel carbonyl on a clean Cu(ll1) surface. Sorption of 0, can be described by a precursor state model for dissociative chemisorption followed by a first order reaction of adsorbed oxygen atoms to incorporated oxygen atoms. The initial sticking probability is 10-a at room temperature and increases with increasing crystal temperature.The first chemisorption of 0, on a freshly prepared alloy surface causes an irreversible surface reconstruction.The amount of oxygen in the near surface layer decreases with increasing crystal temperature.The reaction of sorbed oxygen with H, can be described by a nucleation and growth mechanism with a time dependent number of growth centers. The rate is strongly affected by an operating ionisation gauge.

Cu(lll)-Ni surface alloys were prepared by dissociation of nickel carbonyl on clean Cu(ll1). The adsorption of CO is studied with AES and ellipsometry. At pressures higher than lo-* Pa CO, migration of Ni to surface layers occurs, which makes it impossible to measure adsorption isotherms. The removal of preadsorbed oxygen on Cu(lll)-Ni with CO is also studied with AES and ellipsometry.A reaction scheme is proposed to describe the two different types of reaction curves. At temperatures below 200 o C, the overall apparent activation energy is 40 kJ/mol, at higher crystal temperatures this value drops to 10 kJ/mol. CO is found to react with oxygen on the surface, which is replenished by incorporated (subsurface) oxygen.