An experimental and theoretical study of the valence shell photoelectron spectra of 2-bromothiophene and 3-bromothiophene

The valence shell photoelectron spectra of 2-bromothiophene and 3-bromothio phene have been studied, both experimentally and theoretically, in order to characterise the main bands due to single-hole states and to assess the im portance of electron correlation in the formation of satellite states. Sync hrotron radiation has been employed to measure photoelectron angular distri butions and branching ratios in the photon energy range 13-115 eV, and the results indicate that the photoionisation dynamics of the (12a ')(-1) (B) o ver tilde (2)A ', (2a ")(-1) (C) over tilde (2)A " and (11a ')(-1) (D) over tilde (2)A ' states are affected by Cooper minima. The experimental data d emonstrate that the 12a ' and 2a " orbitals, corresponding to the Br 4p lon e pairs, retain their atomic properties to a substantial degree, and that t he same is true, although to a lesser extent, for the 11a ' orbital which i s related to the S 3p subshell. The results are compared with similar measu rements on chlorothiophene and bromobenzene. The vertical ionisation energi es and spectral intensities of the entire valence shell photoelectron spect rum have been computed using the third-order algebraic-diagrammatic constru ction approximation scheme for the one-particle Green's function. These the oretical predictions have allowed assignments to be proposed for all the pr ominent structure observed in the experimental spectra. The outer valence G reen's function method has also been used and the calculated ionisation ene rgies show good agreement with the experimental values. Mulliken atomic pop ulations have been computed for some of the outer valence orbitals, and the calculated Br 4p and S 3p content possessed by the 12a ', 2a " and 11a ' m olecular orbitals is in accordance with the strength of the Cooper minimum observed in the photoelectron asymmetry parameters associated with these or bitals. (C) 2001 Elsevier Science B.V. All rights reserved.