Photoionization study of the ionization potentials and fragmentation paths of the chlorinated methanes and carbon tetrabromide

The photoionization yields of CH3Cl, CH2Cl2, CHCl3, CCl4, and CBr4 have been measured in the 10–13.5 eV energy range. Ionization potentials and fragment appearance potentials derived from a detailed study of the hot band contribution at 300°K have been obtained. Although CCl4+ is apparently unstable, we have found that CBr4+ is stable. Fragmentation of the chlorinated and brominated methanes in the energy range studied appears to be limited to halogen loss, even though hydrogen loss is in certain cases energetically favored. An argument based on the symmetry of the fragments and the transition state producing these fragments is proposed to account for this observation.