Photoelectron spectra of halogenated ethylenes

Photoelectron spectra of chloro-, fluoro- and chlorofluoroethylenes have been measured. Ionization potentials in the range 6 to 21 eV have been determined, and vibrational structure associated with many of the electronic transitions has been interpreted in terms of vibrations of the ion and correlated with those of the parent molecule. The various ionization potentials have been associated with specific orbitals such as the C=C π orbital, and molecular orbitals derived from the p atomic orbitals of halogens. Variations in these ionization potentials have been discussed in relation to inductive and conjugative effects of the halogen substituents. Some observed differences between the spectra of the chloro- and fluoroethylenes have been considered in relation to possible mechanisms of the changes in bond length consequent upon ionization.