He II photoelectron spectra of diatomic alkali halides

Abstract

He I photoelectron spectra of diatomic alkali halide molecules have been extended by use of the He II 40.8 eV line. Ionization from both the molecular X^–p⁶ shell, previously observed with He I radiation, and the M⁺p⁶ shell, not observed in our earlier work, has been detected and the ionization energies shown to be consistent with predictions based on an essentially ionic molecule. A mechanism involving configuration interaction has been suggested to account for fine structure associated with ionization from the M⁺p⁶ shell. Ionization from the X^–s² shell has not been detected except possibly for CsBr. This is attributed to the low cross section for ionization from this orbital and in some cases is thought to be due to overlap with the M⁺p^–1 structure. Ionization energy measurements are reported for the chlorides, bromides and iodides of caesium, rubidium and potassium.