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 ${\mathrm{CCl}}_4^{+}$ is apparently unstable, we have found that ${\mathrm{CBr}}_4^{+}$ 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.