An experimental and theoretical study of the valence shell photoelectron spectrum of bromobenzene Original Research Article

The valence shell photoelectron spectrum of bromobenzene has been studied, both experimentally and theoretically, in order to characterise the main bands due to single-hole states and to assess the importance of electron correlation in the formation of satellite states. Synchrotron radiation has been employed to measure photoelectron angular distributions and branching ratios in the photon energy range 16–120 eV, and high-resolution spectra have been recorded using He I excitation. The results indicate that the 2b1 and the 6b2 lone-pair orbitals retain their atomic properties to a substantial degree, and that the photoionisation dynamics associated with these two orbitals exhibit effects due to the presence of a Cooper minimum. The results for bromobenzene are compared with corresponding data for benzene and it appears that several of the orbitals remain essentially unperturbed by the introduction of the halogen atom. The high-resolution spectra have enabled detailed assignments to be made of the vibrational structure displayed in the X̃ 2B1, Ã 2A2, B̃ 2B2, C̃ 2B1 and K̃ 2A1 photoelectron bands. Two variations of the many-body Greenʹs function method have been employed to evaluate the ionisation energies and pole strengths (relative intensities) of all valence states. These predictions have helped assign and interpret the features caused by configuration interaction.