Measurement of g factors by quantum beats in the OH free radical

Using pulsed optical excitation we have measured the g factors of twelve hyperfine levels (K=1A throughA 6) of the AI122+ state of OH by observation of quantum beats. The results are consistent with Hund's case (b) coupling to within the experimental uncertainty of 0.35% (principally limited by magnetic field calibration). However, the ratios of the g factors of a given hyperfine doublet, which are independent of field and accurate to about 0.15%, show significant discrepancies from theory.