Partial photoionization cross sections of SF6between 20 and 54 eV: An interpretation of the photoelectron spectrum

The partial photoionization cross sections of sulphur hexafluoride have been measured between 20 and 54 eV using synchrotron radiation. Some of these cross sections are dominated by strong resonance effects. These resonances are shape resonances, resulting from the interaction between the photoelectron and the molecular field and hence always occur at approximately the same photoelectron kinetic energy. Expressed somewhat differently, they are final-state effects and can be thought of as arising from the multiple scattering of the photoelectron. Following Dehmer, the prominent resonance immediately above threshold in S${\mathrm{F}}_6$ is identified as having $g$ symmetry. Hence, only valence orbitals with $u$ symmetry may couple to it. This provides a powerful selection rule, which allows making an assignment of the peaks in the photoelectron spectrum. Even in the absence of resonances, the partial cross sections are qualitatively different for different orbitals. It is argued that measurements and calculations of partial cross sections should, in many cases, yield easier and more unambiguous assignments of peaks in photoelectron spectra than corresponding studies of ionization potentials.