A systematic investigation of the influence of Cooper minima on the photoionisation dynamics of the monohalobenzenes

Abstract

The valence shell photoelectron spectrum of iodobenzene has been studied using HeI and synchrotron radiation. In addition to the main bands associated with the single-hole states, complex satellite structure due to many-electron effects has been observed in the inner valence region. Two variations of the many-body Green’s function method have been employed to evaluate the ionisation energies and pole strengths of all valence states and the results have facilitated an interpretation of the experimental spectra. Photoelectron angular distributions and branching ratios have been determined using monochromated synchrotron radiation in the photon energy range 16–120 eV, and those for the lone-pair orbitals show effects that can be attributed to Cooper minima. However, the influences of Cooper minima have also been observed in the asymmetry parameters associated with other states, and the possible role of interstate mixing is discussed. The present data for iodobenzene are compared with similar measurements for benzene, chlorobenzene and bromobenzene to examine and contrast the effect of the halogen atom substituent. Vibrational structure has been observed in several of the photoelectron bands of iodobenzene excited with HeI radiation and analyses have been performed for the X ̃ 2 B 1 , C ̃ 2 B 1 and D ̃ 2 A 1 ionic states.