The adsorption behavior of CO on bimetallic Ni/Cu͑110͒ surfaces has been studied experimentally by thermal-desorption spectroscopy and theoretically by density-functional theory ͑DFT͒ calculations. The bimetallic surfaces were produced either by evaporation of nickel or by decomposition of Ni͑CO͒ 4 on Cu͑110͒. Adsorption of CO at 180 K on such a bimetallic surface yields three new adsorption states with adsorption energies between that of CO on clean Cu͑110͒ and clean Ni͑110͒. The new

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... peaks from the bimetallic surface, designated as ␤ 1 -␤ 3 , can be observed at 250, 300, and 360 K, respectively. These new states are most pronounced when 1 2 monolayer of nickel is present on the copper surface. DFT calculations, using the Vienna ab initio simulation package code, were performed to identify the most probable Ni/Cu atomic arrangements at the bimetallic surface to reconcile with the experimental results. It turned out that CO adsorption on nickel dimers consisting of in-surface and adjacent subsurface atoms can best explain the observed experimental data. The result shows that CO adsorption is determined by local ͑geometric͒ effects rather than by long-range ͑electronic͒ effects. These findings should contribute to a better understanding of tailoring catalytic processes with the help of bimetallic catalysts.