Polarized fluorescence spectroscopy of O+2

Polarized fluorescence from the A 2Πu and b 4Σ−g states of O+2 following photoionization of O2(X 3Σ−g) in the 17–21 eV region has been employed to determine population alignment in the O+2 photoion. The measured A-channel polarization exhibits pronounced structure which correlates well with the known positions of (autoionizing) Rydberg states, whereas polarization signal in the b channel has broad and less prominent features. The measured b-channel polarization values (ranging from −0.02 to −0.05) are consistent with single-channel calculations, while the A-channel polarization measurements (which range from 0 to 0.09) are of opposite sign to the previously reported single-channel calculations. The results of more involved calculations show that this sign reversal in the A channel can be attributed to the presence of intravalent 3Σ−u states which autoionize into the A channel in the near-threshold region.