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

The photoelectron spectrum of the chlorobenzene molecule has been studied using both monochromated synchrotron radiation with photon energies between 15 and 120 eV and HeI radiation at 21.22 eV. Photoelectron angular distributions and branching ratios have been determined over the entire energy range studied. Theoretical investigations have been performed using ab initio SCF and many-body Green’s function methods to evaluate wave functions, binding energies and relative intensities. The ADC(3) calculations of binding energies and pole strengths were particularly important for the interpretation of the inner valence spectrum where electron correlation effects are found to be important. The main part of the photoelectron spectrum is similar to that of benzene but some of the bands are characteristic of the chlorine atom. The Cooper minimum of the Cl 3p orbital is clearly reflected in some of the bands and is used to assess the mixing between ring orbitals and chlorine atomic orbitals. The HeI-excited spectra show extensive vibrational structure in the X̃ 2B1, Ã 2A2, B̃ 2B2, C̃ 2B1 and K̃ 2A1 photoelectron bands. The vibrational structure is analysed in detail and compared to results obtained from multiphoton ionisation photoelectron spectroscopy.