scattering cross sections and adsorption kinetics

He diffraction and specular He scattering measurements of O on Rh(l l l) were made for Ts = 125-625 K and 0 o = 0.0-0.50 ML. For T s> 450 K and 0 o < 0.21 ML, specular He scattering from the O/Rh ( l l l) overlayer is well described by a model for disordered adsorbates, with a cross section of 62.6.~2 for 63 meV He. At higher coverages, these measurements reveal a complex relationship between coverage, temperature, and the ordered overlayer structures for O/Rh(111). In addition, adsorption isotherms presented here show second order Langmuir adsorption kinetics for O 2 on Rh ( l l l) and a sticking coefficient of about 5 % for O 2 on 525 K Rh(ll 1)