Structural reanalysis of the Rb(111)+(root 3x root 3)R30 degrees-CO and Rh(111)+(2x2)-3CO phases using automated tensor LEED

The structures of Rh(111)+(root 3 x root 3)R30-CO and Rh(111)+(2 x 2)-3CO have been reanalyzed using automated tensor LEED. In accordance with the result of an earlier LEED analysis: the CO molecules were found to occupy top sites in Rh(111)+ (root 3 x root 3)R30-CO; for the topmost substrate layer, a buckling is non determined, with the Rh atom underneath CO being pulled out by 0.08 Angstrom. In the (2 x 2)-3CO structure, the CO molecules are found to occupy top sites and three-fold hollow sites, in contrast to results of an earlier LEED analysis. These findings are in line with recent core electron spectroscopy experiments, but are at odds with earlier conclusions from vibrational spectroscopy where assignment was made to top and bridge sites. Together with other metal-CO and metal-NO systems described in the literature, the Rh(111)+(2 x 2)-3CO phase demonstrates that great care has to be taken in adsorption site assignment using the C-O and N-O stretch frequencies. (C) 1997 Elsevier Science B.V.