Shape-resonance-induced non-Franck--Condon effects in (2+1) resonance enhanced multiphoton ionization of the C 3Pi/sub g/ state of O2

We show that strong non-Franck--Condon effects observed in (2+1) resonance enhanced multiphoton ionization of the C 3Pi/sub g/ state of O2 are due to the kσ/sub u/ shape resonance previously observed in single-photon studies of diatomic molecules. Calculated vibrational branching ratios for the v' = 2,3 levels of the C 3Pi/sub g/ state are in reasonable agreement with experiment. Certain discrepancies remain in comparing theoretical results with the measured spectra, and possible electron-correlation effects which underly this are discussed