An experimental and theoretical study of the valence shell photoelectron spectrum of oxalyl chloride

Polarization dependent photoelectron spectra encompassing the outer valence orbitals of oxalyl chloride have been recorded in the photon energy range 19 – 91 eV. These have allowed photoelectron anisotropy parameters and branching ratios to be determined. Photoionization partial cross sections and photoelectron anisotropy parameters have been calculated with the Continuum Multiple Scattering – Xα approach. Four of the outer valence orbitals are predicted to possess a significant Cl 3p lone-pair character and have closely grouped binding energies. The photoionization dynamics of these four orbitals are predicted to be strongly affected by the Cooper minimum associated with the Cl 3p orbital in the isolated atom at photon energies around 40 eV. A comparison between the theoretical and measured photoelectron anisotropy parameters has enabled the molecular orbital sequence to be clarified. A doublet has been observed in the region of the photoelectron spectrum where a band due to the 5bu orbital might be anticipated. Our calculations indicate that the 6bu and 5bu orbitals are coupled. This coupling may account for the apparent lack of a pronounced Cooper minimum in the β-parameter associated with the nominal 6bu ionization and for the unexpected appearance of the adjacent photoelectron band, nominally associated with the 5bu orbital. The vertical ionization energy of the outermost 7ag orbital was experimentally determined to be 11.266±0.005 eV