MULTIPLET-SPECIFIC SHAPE RESONANCE AND AUTOIONIZATION EFFECTS IN (2+1) RESONANCE ENHANCED MULTIPHOTON IONIZATION OF O-2 VIA THE D1-PI-G STATE

In this paper we discuss the single-photon ionization dynamics of the d 1Πg Rydberg state of O2. Comparision is made with vibrationally resolved measurements of photoelectron spectra which employ (2 + 1 ) resonance enhanced multiphoton ionization (REMPI) through the d 1Πg state. A σu shape resonance near the ionization threshold leads to non-Franck-Condon vibrational branching ratios and a substantial dependence of photoelectron angular distributions on the vibrational state of the X 2Πg ion. Significant differences exist between our one-electron predictions and experiment. These are mainly attributed to electronic autoionization of repulsive 1Σu- , 1Σ u+ , and 1Δu states associated with the 1πu3 1πg3, configuration. A proposed singlet "K" 1Πu Rydberg state converging to the A 2Πu ion probably also contributes to autoionization in the d 1Πg state spectrum. We also show that autoionizing H and J 3Πu Rydberg states of O2 converging to the a 4Πu and A 2Πu ionic thresholds, respectively, may play a previously unsuspected role in the C 3Πg state one-color REMPI spectra. We discuss multiplet-specific (spin-dependent) effects via comparision of these results with recent experimental and theoretical studies of O2 C 3Πg photoionization. © 1990 American Institute of Physics.