Near-threshold behavior of theK-shell satellites in CO

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 K-shell satellites were measured. Eight different C 1s satellite states were identified, showing very complex threshold behavior. The resonancelike behavior of the (2σ${)}^{\mathrm{-}1}$(1π${)}^{\mathrm{-}1}$(2${\mathrm{\pi }}^{\mathrm{*}}$ ${)}^1$(S’=1) satellite BR agrees with recent theoretical calculations. The observed energy dependence of the singlet (2σ${)}^{\mathrm{-}1}$(1π${)}^{\mathrm{-}1}$(2${\mathrm{\pi }}^{\mathrm{*}}$ ${)}^1$ satellite compares less well with the calculations. Three ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ satellites with a (2σ${)}^{\mathrm{-}1}$(5σ${)}^{\mathrm{-}1}$(nσ${)}^1$ configuration have a constant satellite BR over the energy range studied. Three 2σ satellites, which have been assigned as pure conjugate shake-up states, have intensity only near threshold. The threshold spectrum above the O 1s 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 ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ satellites, which have been described by configuration interaction of (1σ${)}^{\mathrm{-}1}$(5σ${)}^{\mathrm{-}1}$(nσ${)}^1$ states with a singlet π${\mathrm{\pi }}^{\mathrm{*}}$ state, show indications of shape-resonance-like behavior.