Theory of vibrationally inelastic electron scattering from oriented molecules

Abstract

The electron scattering cross sections, both elastic and vibrationally inelastic, have been calculated using the $X\ensuremath{\alpha}$ multiple-scattering method for ${\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$, and CO. The accuracy of the calculational scheme is tested by comparing to data from gas-phase measurements. Good agreement is found between theory and experiment. The formalism is then applied to molecules with fixed orientation by freezing out the rotational motion. The differential inelastic scattering cross sections for vibrational excitation exhibit a variety of angular patterns depending upon the molecule and the energy and direction of the exciting electrons. In all cases which have been calculated, the cross section for vibrational excitation is dominated by negative-ion resonances. The angular distribution patterns reflect the symmetry of these ionic states. These calculations indicate the possibilities of using the characteristics of the inelastic-cross-section patterns as a function of the exciting electrons' energy and direction to study molecules adsorbed on a surface.