Low-energy electron scattering from CH₄, C₂H₄and C₂H₆

Abstract

Low-energy electron scattering by CH4, C2H4 and C2H6 has been studied using two different synchrotron radiation photoionization spectrometers. The variation in the total scattering cross section with energy was measured in a transmission experiment at Super-ACO, LURE, Orsay, France and electron scattering spectra were recorded with a crossed-beam apparatus at the Synchrotron Radiation Source (SRS), Daresbury Laboratory, UK. Interest was focused on the energy range below 2 eV where previously unrecorded threshold vibrational resonances were observed. The energy dependencies of the observed total and elastic scattering cross sections below 1 eV were analysed by the modified effective-range theory (MERT). Excitation functions for vibrationally inelastic processes in CH4 and C2H4 were measured and shown to depart radically from the predictions of the first-order Born approximation.