Dresden 2006 – scientific programme

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O: Oberflächenphysik

O 46: Adsorption VI

O 46.4: Talk

Friday, March 31, 2006, 12:00–12:15, TRE Phys

CO adsorption and CO and O coadsorption on Rh(111) — •Robert Schennach¹ and Imre Bako² — ¹Institute of Solid State Physics, Graz University of Technology, Graz, Austria — ²Chemical Research Institute of the Hungarian Academy of Sciences, Budapest, Hungary

The adsorption of CO and the coadsorption of CO and O on Rh(111) at 123 K was studied using reflection absorption infra red spectroscopy (RAIRS) and density functional theory (DFT). CO adsorption on Rh(111) proceeds via adsorption at on top sites at low coverages (less than 0,33 monolayer (ML)) and by on top and hollow site occupation at higher coverages (more than 0,33 ML). Evidence from the RAIRS measurements shows that also some bridge sites are occupied from intermediate coverages up to a full monolayer. A new vibration in the on top region around 2085 cm⁻¹ is found in the IR spectra at higher coverages, which has not been detected in high resolution electron energy loss spectroscopy (HREELS) studies. The origin of this new vibrational feature is discussed in detail using the results from DFT calculations. Experiments show that this new vibration vanishes during CO adsorption at elevated temperatures. Coadsorption of oxygen generally leads to a shift to higher wavenumbers of the CO vibrations. This is explained in terms of increased repulsive interactions between the adsorbed species. The adsorption sequence does not influence the vibrational spectra, however, the CO to O ratio and the surface temperature during adsorption show an influence. Thermal desorption from the coadsorbed layers shows some reaction between CO and O to form CO₂.