Absorption intensities of rovibronic transitions in the A-band of 16O2: Analysis and calculation of magnetic dipole and electric quadrupole contributions

•The measured M1 transition intensities in the A-band of O2 theoretically analyzed.•We get the value 〈M1〉=0.0268 μB for the M1 transition moment.•This is close to the ab initio value 0.02552 μB.•The E2 contribution to line intensities is also calculated.

The recently measured magnetic dipole (M1) absorption intensities of rovibronic transitions in the A-band (bΣg+1−XΣg−3, 030 band) of 16O2 are theoretically analyzed employing a model in which the bΣg+1:XΣg−3 mutual perturbations are treated to a sufficient degree of accuracy. Effects of rotational perturbations became manifest in the data analysis and rovibronic correction parameters are needed to reconcile theory and experiment. At a subtle level there is evidence of Herman-Wallis (HW) type effect arising from vibration-rotation interaction in the b and X states. The functional form for the HW correction factor is arrived at from first principles. The final calculations reproduce the measured intensities to fraction of a percent, well within the measurement accuracy. The present analysis leads to the value 〈M1〉0,0=0.02679(4) μB for the M1 transition moment, and the spontaneous emission rate (Einstein-A coefficient) Γ0,0=0.0874 s−1. For the sake of completeness, the electric quadrupole (E2) contribution to the observed intensities is also quantitatively assessed.