Calculations of the partial differential photoionization cross sections for the valence bands of ethylene

Abstract

Partial photoionization cross sections and the angular distribution parameter, β, have been calculated for the six valence orbitals of ethylene using the multiple-scattering Xα method. The calculations cover the energy range from 1.36 eV above the ionization threshold to 50 eV photon energy for each orbital. Shape resonances were found in both the b 1u and b 2u continuum channels near the ionization threshold. Within the electric dipole selection rule these resonances would influence photoionization from the 1b 3g-3a g and 2a g orbitals. A very broad maximum in the cross section was found in the b 3g continuum channel associated with ionization from the 2b 1u orbital. The presence of resonances in or near the ionization continuum is discussed in terms of the possible molecular orbitals generated in a minimum basis set LCAO calculation. Although the exact position of resonances cannot be obtained this way, it is possible to predict the possible presence of shape resonances and the orbitals likely to be involved. Based on the results of the calculations the potential use of the angular distribution parameter for orbital assignments is discussed.