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.