Temporary pi* and sigma* anions and dissociative electron attachment in chlorobenzene and related molecules

Coupled-cluster, Hartree-Fock, and B3LYP calculations are employed to study the gas-phase empty-level structures of chlorobenzene, benzyl chloride, an d (2-chloroethyl)benzene. All three theoretical approaches reproduce accura tely the energy trends of vertical electron attachment observed in the elec tron transmission spectra and predict the occurrence of the lowest sigma* r esonance about 2 eV higher in energy than the lowest pi* resonance, in cont rast with a recent suggestion by others. The relative cross:sections for di ssociative electron attachment are measured in the benzene derivatives and in saturated chlorohydrocarbons. The Cl- currents and a comparison of the e nergies of maximum production in the dissociative attachment spectra with t he resonance energies located in the electron transmission spectra clearly indicate, that in the benzene derivatives, dissociation follows electrontra pping into a ring pi* empty orbital and subsequent intramolecular transfer to the chlorine atom, in line with the conclusions of an earlier work.