An experimental and theoretical study of the valence shell photoelectron spectra of thiophene, 2-chlorothiophene and 3-chlorothiophene

The valence shell photoelectron spectra of thiophene, 2-chlorothiophene (2- Cl-Th) and 3-chlorothiophene (3-Cl-Th) have been investigated theoretically and experimentally, The third-order algebraic-diagrammatic construction ap proximation scheme for the one-particle Green's function has been employed to evaluate the vertical ionisation energies and spectral intensities. The ground state geometrical parameters of the three molecules have been optimi sed at the level of the second order Moller-Plesset perturbation theory, an d standard cc-pvDZ basis sets have been used throughout. The results for th e outer valence region of thiophene agree well with available experimental and theoretical data. Very satisfactory agreements have been obtained betwe en the theoretical predictions for the photoelectron spectra of 2-Cl-Th and 3-Cl-Th and the corresponding experimental data recorded in the present st udy. Assignments have been proposed for the major spectral structures, In a ll three molecules the breakdown of the molecular orbital ionisation pictur e associated with the pi (1) molecular orbital is discussed, Synchrotron radiation has been used to record the complete valence shell ph otoelectron spectra of 2-Cl-Th and 3-Cl-Th. Photoelectron angular distribut ions and branching ratios have been determined in the photon energy range 1 3-115 eV, and those for the chlorine and sulphur 3p orbitals show effects t hat can be attributed to Cooper minima. A high resolution photoelectron spe ctrum of the outer valence shell of 2-Cl-Th has been recorded using HeI rad iation, and vibrational structure has been observed and analysed in the (X) over tilde (2)A " (A) over tilde (2)A ", (B) over tilde (2)A', (C) over ti lde (2)A " and (I) over tilde (2)A' state bands. (C) 2001 Elsevier Science B.V. All rights reserved.