STRUCTURAL REANALYSIS OF THE RB(111)-3X-ROOT-3)R30-DEGREES-CO AND RH(111)+(2X2)-3CO PHASES USING AUTOMATED TENSOR LEED((ROOT)

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 wi th 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 topm ost substrate layer, a buckling is non determined, with the Rh atom un derneath CO being pulled out by 0.08 Angstrom. In the (2 x 2)-3CO stru cture, the CO molecules are found to occupy top sites and three-fold h ollow sites, in contrast to results of an earlier LEED analysis. These findings are in line with recent core electron spectroscopy experimen ts, but are at odds with earlier conclusions from vibrational spectros copy where assignment was made to top and bridge sites. Together with other metal-CO and metal-NO systems described in the literature, the R h(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 frequencie s. (C) 1997 Elsevier Science B.V.