Vibrational excitation of ethylene by electron impact: 1–11 eV

Abstract

Differential cross sections for vibrational excitation of ground state C2H4 and C2D4 by electron impact have been studied with a crossed-beam apparatus for electron energies between 1 and 11 eV. The scattering is dominated by two resonance regions in which the vibrational cross sections of totally symmetric modes are preferentially enhanced to the order of 10−16 cm2. The first resonance region is centered near 1.8 eV. Here all energy-loss spectra and energy and angular dependences of cross sections can be accounted for by a 2B2g shape resonance of an intermediate lifetime. The second resonance region centered near 7.5 eV is very broad. The dominant vibrational modes and the corresponding angular distributions are distinctly different from those in the lower region. We interpret this second region in terms of short-lived shape resonances, the dominant one being a 2Ag compound state comprising the target molecule plus an electron in the 4ag orbital.