Very low-energy electron scattering from benzene: experiment and theory

Low-energy collision studies have shown that the scattering cross section for electrons by benzene rises sharply at electron impact energies below similar to200 meV. This was attributed in earlier work to electron attachment and formation of benzene anions with lifetimes tau > 1 mus. A detailed study of electron attachment to benzene is reported here that makes use of Rydberg atom techniques. The data provide no evidence for the formation of long-lived benzene anions, although a small collisional ionization signal is observed which is consistent with the formation of short-lived excited anions (tau less than or equal to 3 ps). An alternative explanation for the rapid rise in cross section at low energy is presented, based on ab initio scattering calculations. These calculations indicate that virtual state scattering takes place at low energies. Possible implications of this are briefly discussed.