Theoretical study of shape resonances in the partial photoionization cross sections for the b  4Σ g − and B  2Σ g − states of O2

Using the single-center static-exchange approximation, the 3σg photoionization cross section of O2 is calculated. The R-averaged results are obtained for the production of O+2 in the b 4Σ−g and B 2Σ−g states. Shape resonances, a few electron volts wide, are found at 3 and 2.5 eV from the threshold for these two states, respectively. We find reasonable agreement with the experimental cross sections for the B 2Σ−g state and with the β values for the b 4Σ−g state. For this last state, comparison between theory and experiment leads us to a possible interpretation of the data, but a definite answer can not be given without taking into account the autoionized Rydberg states.