An interesting and intensively studied bimetallic system is that of Cu-Pd. In fact, Cu and Pd form binary alloys with two ordered structures: B2 of Cu-Pd and L1 2 of Cu 3 Pd . The Cu-Pd alloys are a practical catalyst for alkene oxidation [2], ethanol decomposition [3], water gas shift reaction [4], reducing automobile-exhaust pollutants , and for methanol synthesis . Great interest has arisen in the bimetallic surface that is formed through vacuum deposition of one metal on the single crystal substrate of another metal because such a surface is an attractive template for studying not only surface alloy structures but also catalytic activities, which differ from those of individual surfaces . Two types of ordered surface structures are known to be formed on a Cu(1 0 0) substrate by vacuum deposition of Pd: a half-monolayer (ML)-thick and a onemonolayer-thick Pd deposition, respectively, generate Cu(1 0 0)c(2 ร 2)-Pd and Cu(1 0 0)-(2 ร 2)p4g-Pd . Related to Pd depositions on Cu(1 1 1), several reports have been published ; recent reflection by high-energy electron diffraction (RHEED) investigation reveals that Pd grows initially with in-plane Cu(1 1 1) lattice parameter and the parameter reaches the value of clean Pd(1 1 1) with increasing coverage. Regarding Cu(1 1 0), alloying behaviors of the deposited Pd and substrate Cu atoms have been reported using a scanning tunneling microprobe (STM), X-ray photoelectron spectroscopy (XPS), lowenergy electron diffraction (LEED), and temperature programmed desorption (TPD) . The dynamic behavior of probe molecules, e.g. carbon monoxide (CO) at the Pd/Cu(1 1 0) surface, would cast some light not only on its surface chemistry but also on the atomic structure of the outermost surface because Pd and Cu atoms at the top surface of Pd/Cu(1 1 0) should have different properties for adsorption and desorption of the probe molecule.
Infrared reflection absorption spectroscopy (IRRAS) is useful for the study of vibrational states of the adsorbate. The frequency and the width of bands caused by adsorbate are quite sensitive to the surface properties, giving us information related not only to the surface chemistry of adsorbates, but also that related to the surface atomic structure of the binary metal surface. It has been demonstrated that carbon monoxide (CO) is useful to probe surface lattice structures of the metal. Surface lattice structures can be evaluated using LEED, RHEED, and/or STM, whereas IRRAS spectra