A study of the valence shell electronic structure and photoionisation dynamics of ortho-dichlorobenzene, ortho-bromochlorobenzene and trichlorobenzene

Abstract

The valence shell electronic structure and photoionisation dynamics of ortho-dichlorobenzene, ortho-bromochlorobenzene and trichlorobenzene have been investigated both experimentally and theoretically. Angle resolved photoelectron spectra of ortho-dichlorobenzene have been recorded using synchrotron radiation in the photon energy range from close to threshold to 100eV. The photoelectron anisotropy parameters derived from these spectra have been compared to predicted values obtained with the continuum multiple scattering approach. The comparison demonstrates that ionisation from some of the orbitals is influenced by the Cooper minimum associated with the chlorine atom. High resolution photoelectron spectra of the outer valence orbitals of ortho-dichlorobenzene and ortho-bromochlorobenzene have been recorded with HeI radiation and the observed structure has been interpreted using calculated ionisation energies and spectral intensities. Electron correlation affects ionisation of the inner valence orbitals and leads to satellite formation. Simulations of the X̃2B1,Ã2A2 and B̃2B2 state photoelectron bands in ortho-dichlorobenzene have enabled most of the vibrational progressions appearing in the experimental spectrum to be assigned. Photoelectron spectra of trichlorobenzene have also been measured and the anisotropy parameters associated with some of the outer valence orbitals exhibit a photon energy dependence which resembles that predicted for atomic chlorine. This behaviour is consistent with the theoretically predicted character of these orbitals.