PHOTO-DISSOCIATION SPECTROSCOPY OF HALOGEN-SUBSTITUTED BENZENE IONS

Photodissociation spectra of the four halobenzene gas-phase parent ions are presented, obtained by a combination of one-photon and two-photon photodissociation. The spectra are compared with the corresponding halotoluene ion spectra, with the photoelectron spectra of neutrals, and with theory. The close similarity of halobenzene and halotoluene spectra indicates a minor perturbing role for the methyl group. It is concluded from the analysis that the fluorine substituent has little or no spectroscopic manifestation but that, in the other halobenzene ions, the halogen substituent plays an important spectroscopic role, in particular contributing a prominent spectral feature having halogen-to-ring charge transfer character. Comparison of peak positions in the photodissociation and photoelectron spectra in the bromobenzene and iodobenzene cases suggests that the ion ground state is substantially distorted relative to the neutral molecule. © 1979, American Chemical Society. All rights reserved.