CO Adsorption on c(2×2)-Li/Cu(100): interaction between CO and Li on unreconstructed Cu(100) surfaces

CO adsorption on the Cu(100)-c(2×2)-Li surface was studied using high resolution electron energy loss spectroscopy (HREELS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD) to examine the interaction between CO and Li and the properties of an Li–CO complex on unreconstructed Cu(100) surfaces. The ν(CuLi) peak appeared at 310 cm−1 for the c(2×2)-Li surface with unreconstructed Cu substrate, in addition to a peak at 710 cm−1 which was not observed on the Cu(100)-(2×1)-Li surface with a missing-row structure. CO stretching modes appeared at 1200, 1860 and 2040 cm−1 when the c(2×2)-Li surface of 0.3 ML Li coverage was exposed to CO at 130 K. It is considered that these correspond to the Li–CO complex and CO molecules adsorbed at bridge and atop sites respectively. The 1200 cm−1 peak decreased in intensity when the surface was almost saturated with CO. It was proved from the result of the experiment using 13C18O that the Li–CO complex collapses and changes to the CO adsorbed at atop and bridge sites. The ν(CO) of 1200 cm−1 observed in the present study comes in the category which is the lowest among systems of other alkali metals, whereas the CO desorption temperature rises only by 15 K.