Molecular beam studies of sticking of oxygen on the Rh(111) surface

The sticking coefficients of oxygen on the Rh(111) surface have been measured using O-2 molecular beams seeded with different rare gases to achieve beam energies in the range E-i = 25 - 600 meV. With increasing O-2 incident beam energy, the adsorption evolves continuously from a molecular precursor-mediated process at low energies to a direct adsorption process described by Langmuir kinetics at high energies. The analysis of the dependence of the initial sticking coefficient on the incident kinetic energy and the angle of incidence as well as on the surface temperature provide information on important parameters of the potential energy surface. Further insight into the nature of the adsorbed species could be obtained from the UPS measurements of the adsorption induced work function changes and from helium atom diffraction measurements of structural modifications as a function of the kinetic energy angle of incidence of the oxygen molecules, and the surface temperature. The ''simple washboard'' model accounts for the trapping well of the molecular precursor and is able to describe many of the observed features in the precursor region. (C) 1997 American Institute of Physics.