Adsorption of CO on Rh(100) studied by infrared reflection-absorption spectroscopy

The interaction of CO with a Rh(100) surface at 90 and 300 K has been investigated with infrared reflection–absorption spectroscopy (IRAS). Absorption bands due to the C–O stretch are found in both the linear and bridging regions at all coverages for both adsorption temperatures. For adsorption at 300 K, an ordered CO layer is formed at ∼0.4 monolayers (ML) as evidenced by a sharp, highly symmetrical, linear-CO band. At θCO>0.45 ML, the reduction in intermolecular separation and increasing intermolecular repulsive forces in the CO adlayer are evidenced by the increased broadness of both the linear- and the bridged-CO bands. CO adsorption at 90 K yields a nonuniform adlayer dominated by island formation at θCO