NEAR-THRESHOLD BEHAVIOR OF THE K-SHELL SATELLITES IN CO

The study of photoelectron satellites in the near-threshold region is important for differentiating among various electron correlation mecha nisms. For CO, which is a prominent test case for theories describing electron correlation effects, the threshold and near-threshold branchi ng ratios (BR's) of the K-shell satellites were measured. Eight differ ent C ls satellite states were identified, showing very complex thresh old behavior. The resonancelike behavior of the (2sigma)-1(1pi)-1(2pi )1(S'=1) satellite BR agrees with recent theoretical calculations. The observed energy dependence of the singlet (2sigma)-1(1pi)-1(2pi)1 sa tellite compares less well with the calculations. Three 2SIGMA+ satell ites with a (2sigma)-1(5sigma)-1(nsigma)1 configuration have a constan t satellite BR over the energy range studied. Three 2sigma satellites, which have been assigned as pure conjugate shake-up states, have inte nsity-only near threshold. The threshold spectrum above the O 1s ioniz ation threshold consists of two distinct groups of satellites. Conjuga te shake-up transitions contribute to the intense feature centered at 551-eV binding energy, which is not observed above its threshold. Two 2SIGMA+ satellites, which have been described by configuration interac tion of (1sigma)-1(5sigma)-1(na)1 states with a singlet pipi state, s how indications of shape-resonance-like behavior.