Infrared reflection absorption study of carbon monoxide adsorption on Cu(1 0 0)-(2 × 2)p4g-Pd ordered alloy surface

Carbon monoxide (CO) adsorption on a Cu(1 0 0)-(2 × 2)p4g-Pd surface was investigated using infrared reflection absorption spectroscopy (IRRAS). The IRRAS spectra recorded during CO exposure to the room-temperature p4g surface show that marked absorptions that are ascribable to linearly bonded and bridge-bonded CO on Pd atoms dominate the spectra. In contrast, when the p4g surface is exposed to CO at 90 K, those two absorption bands appear first. Subsequently, a new band emerges at the high-frequency side of the linearly bonded CO-Pd band. The new band increases in intensity with further CO exposure, accompanied by a reduction in the CO-Pd band intensity. Based on IRRAS results obtained by heating the substrate, additional adsorption of CO onto the Cu atom surrounded by the CO-adsorbed Pd atoms correlates to the new band. The outermost atomic structure of the p4g surface is discussed based on those IRRAS results.