Penning ionization of dichloroethylenes by collision with He*(2³S) metastable atoms

Penning ionization of trans-, cis-, and iso-dichloroethylenes upon collision with metastable He*(2³S) atoms was studied by collision-energy resolved Penning ionization electron spectroscopy. Partial ionization cross sections are found to be larger for ionization from orbitals having Cl 3p characters. Out-of-plane molecular orbitals having Cl 3p characters are especially reactive with the metastable helium atom. Interaction potentials between the target molecules and the He* atom were found to be highly anisotropic. In the Penning ionization electron spectrum of iso-dichloroethylene, an extra band was found and ascribed to an electron correlation band due to a π-π* excitation upon ionization from the highest occupied π orbital.