Near-threshold behavior of the K-shell satellites in CO.

Abstract

The study of photoelectron satellites in the near-threshold region is important for differentiating among various electron correlation mechanisms. For CO, which is a prominent test case for theories describing electron correlation effects, the threshold and near-threshold branching ratios (BR's) of the [ital K]-shell satellites were measured. Eight different C 1[ital s] satellite states were identified, showing very complex threshold behavior. The resonancelike behavior of the (2[sigma])[sup [minus]1](1[pi])[sup [minus]1](2[pi][sup *])[sup 1]([ital S][prime]=1) satellite BR agrees with recent theoretical calculations. The observed energy dependence of the singlet (2[sigma])[sup [minus]1](1[pi])[sup [minus]1](2[pi][sup *])[sup 1] satellite compares less well with the calculations. Three [sup 2][Sigma][sup +] satellites with a (2[sigma])[sup [minus]1](5[sigma])[sup [minus]1]([ital n][sigma])[sup 1] configuration have a constant satellite BR over the energy range studied. Three 2[sigma] satellites, which have been assigned as pure conjugate shake-up states, have intensity only near threshold. The threshold spectrum above the O 1[ital s] ionization threshold consists of two distinct groups of satellites. Conjugate shake-up transitions contribute to the intense feature centered at 551-eV binding energy, which is not observed above its threshold. Two [sup 2][Sigma][sup +] satellites, which have been described by configuration interaction of (1[sigma])[sup [minus]1](5[sigma])[sup [minus]1]([ital n][sigma])[sup 1] states with a singlet [pi][pi][sup *] state, showmore » indications of shape-resonance-like behavior.« less