ANGULAR-DISTRIBUTIONS IN RESONANCE ELECTRON-SCATTERING BY ORIENTED PHYSISORBED MOLECULES - O-2 AG(110)/

We present an experimental and theoretical study of the angular distri bution of electrons resonantly scattered by physisorbed O-2/Ag(110). T he shape of the angular distribution, obtained from high-resolution el ectron energy-loss spectra (HREELS), changes as the coverage is increa sed from the monolayer to the multilayer regime. With the aid of a cla ssical model which takes into account both the azimuthal and polar ori entation of the molecule with respect to the surface and employs struc tural parameters deduced from X-ray absorption experiments, we find th at this result can be attributed to a change in orientation of the mol ecules in the multilayer compared with the monolayer regime.