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

The valence shell photoelectron spectrum of iodobenzene has been studied us ing HeI and synchrotron radiation. In addition to the main bands associated with the single-hole states, complex satellite structure due to many-elect ron effects has been observed in the inner valence region. Two variations o f the many-body Green's function method have been employed to evaluate the ionisation energies and pole strengths of all valence states and the result s have facilitated an interpretation of the experimental spectra. Photoelec tron angular distributions and branching ratios have been determined using monochromated synchrotron radiation in the photon energy range 16-120 eV, a nd those for the lone-pair orbitals show effects that can be attributed to Cooper minima. However, the influences of Cooper minima have also been obse rved in the asymmetry parameters associated with other states, and the poss ible role of interstate mixing is discussed, The present data for iodobenze ne are compared with similar measurements for benzene, chlorobenzene and br omobenzene to examine and contrast the effect of the halogen atom substitue nt. Vibrational structure has been observed in several of the photoelectron bands of iodobenzene excited with HeI radiation and analyses have been per formed for the (X) over tilde(2)B(1), (C) over tilde(2)B(1) and (D) over ti lde(2)A(1) ionic states. (C) 2000 Elsevier Science B.V. All rights reserved .