Adsorption dynamics for CO, CO-clusters and H2 (D2) on rhodium(111)

On Rh(111), carbon monoxide exhibits a sticking coefficient independent of the angle of incidence, decreasing with beam energy. Modulated beam experiments indicate that, at least in the low-energy regime, chemisorption is precursor-mediated. The sticking probability is independent of coverage for the condensed phases of CO adsorption only; for the disordered phase existing at coverages below 0.25 ML, extrinsic precursors are unimportant. CO molecules incorporated into clusters show sticking coefficients considerably smaller than single molecules. For the adsorption of hydrogen, strong rotational effects exist that lead to an isotope effect between H-2 and D-2. At high beam energies, a fine structure in the functional dependence of the sticking coefficient versus beam energy can be seen. (C) 1999 Published by Elsevier Science B.V. All rights reserved.