An experimental and theoretical investigation of the valence shell photoelectron spectrum of cyanogen chloride

The valence shell photoelectron spectrum of cyanogen chloride has been studied using HeI and synchrotron radiation. In the outer valence region the molecular orbital model of ionization holds, and the main bands can be associated with single-hole states. However, in the inner valence region electron correlation effects become important, and these result in complex satellite structure being observed. Vertical ionization energies and spectral intensities have been computed using the Greenʹs function approach, and the results have facilitated an interpretation of the experimental spectra. Photoelectron angular distributions and branching ratios have been measured and have been used to assess the bonding characteristics of the outer valence molecular orbitals. The experimental data for the 8† orbital display an energy dependence which suggests that photoionization from this orbital may be influenced by the chlorine 3p Cooper minimum. The extent to which the 8† orbital can be considered as a chlorine atom lone-pair is discussed. Vibrational structure has been observed in the X2€, $2~+ and B2 € photoelectron bands recorded with HeI radiation, and has been assigned to progressions involving the ?1+ and ?3+ modes.