MOLECULAR-BEAM STUDIES OF STICKING OF OXYGEN ON THE RH(111) SURFACE

The sticking coefficients of oxygen on the Rh(111) surface have been m easured 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 adsor ption process described by Langmuir kinetics at high energies. The ana lysis of the dependence of the initial sticking coefficient on the inc ident kinetic energy and the angle of incidence as well as on the surf ace temperature provide information on important parameters of the pot ential 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 measur ements of structural modifications as a function of the kinetic energy angle of incidence of the oxygen molecules, and the surface temperatu re. The ''simple washboard'' model accounts for the trapping well of t he molecular precursor and is able to describe many of the observed fe atures in the precursor region. (C) 1997 American Institute of Physics .