Multiphoton ionization of O2 X 3Σ−g, a 1Δg, and b 1Σ+g via the two-photon resonant n sσg, n dσg, and n dπg Rydberg levels

Multiphoton ionization spectra have been obtained and analyzed for excitation in the 215–360 nm region from the X 3Σ−g, a 1Δg, and b 1Σ+g states of O2. The 0–0 band of the C 1Πg state is reported for the first time. Measurements of other vibrational bands terminating in the C 3Πg and d 1Πg states are in good agreement with determinations by other groups. Several vibrational levels (v′=0–5) of the 3dπg Rydberg complex have been assigned on the basis of (1) an analysis of the spin–orbit couplings between the (Λ,S) basis-set states, (2) spectral simulation, and (3) the behavior of the states when the excitation radiation is changed from linear to circular polarization.