Interaction of carbon monoxide with bimetallic overlayers

Interaction of carbon monoxide with a few chosen bimetallic overlayers has been investigated along with the core-level binding energies of the deposited metals by employing X-rays as well as UV photoelectron spectroscopies. Core-level binding energies of the deposited metals around monolayer coverages (0 similar to 1) are significantly different than those at high coverages or of the pure metals. Bimetallic overlayers such as Ni/Au and Cu/Pt showing large negative shifts in the surface core-level binding energy of the deposited metal interact strongly with carbon monoxide. In the case of Ni/Au (0(Ni) similar to 0.85), CO dissociates around 280 K. In contrast to this behavior, the interaction of CO with Pd/Mo or W, showing large positive shifts in the surface core-level binding energy, is very weak, and the CO desorption temperature is much lower than that from the clean Pd metal surface. The CO desorption temperature generally increases as the surface core-level shift of the deposited metal becomes more negative; the separation between the (5 sigma + 1 pi) and 4 sigma levels of CO also increases in this direction. These results suggest that the variation in the strength of interaction of CO with bimetallic overlayers is a chemical manifestation of the shift in the surface core-level binding energies of the deposited metals at monolayer coverages.