HELIUM SCATTERING FROM O ON RH(111) - SCATTERING CROSS-SECTIONS AND ADSORPTION-KINETICS

He diffraction and specular He scattering measurements of O on Rh(111) were made for T-S=125-625 K and theta(O)=0.0-0.50 ML. For T-S>450 K a nd theta(O)<0.21 ML, specular He scattering from the O/Rh(111) overlay er is well described by a model for disordered adsorbates, with a cros s section of 62.6 Angstrom(2) for 63 meV He. At higher coverages, thes e measurements reveal a complex relationship between coverage, tempera ture, and the ordered overlayer structures for O/Rh(111). In addition, adsorption isotherms presented here show second order Langmuir adsorp tion kinetics for O-2 on Rh(111) and a sticking coefficient of about 5 % for O-2 on 525 K Rh(111).