RESONANCE ELECTRON-SCATTERING BY ORIENTED O-2, N-2, AND CO AND APPLICATION TO PHYSISORPTION ON GRAPHITE

In this paper, we explore the connections between resonance electron scattering by isolated and physisorbed molecules. The multiple scattering Xalpha method is used to calculate cross sections for electron scattering via the sigma shape resonances of O2, N2, and CO, near 9, 22, and 20 eV, respectively. Special emphasis is placed on the O2 resonance, for which no previous theoretical work has been reported. In all three cases, quantitative agreement is obtained with experimental gas phase scattering results. Angular distributions are then calculated for the isolated, oriented molecules, and compared with the angular distributions recently observed in resonance scattering by O2, N2, and CO molecules oriented by physisorption on graphite. Characteristic nodes observed in each of the angular distributions are related to the calculated angular profiles, together with a previously proposed selection rule which we now formalize. This scheme allows the orientation of the molecules on the surface to be determined.