We measured unperturbed frequency of Doppler-broadened molecular transition in O2 B band with relative uncertainty of 2*10-11 . We obtained absolute transition frequency with uncertainty typical for Doppler-free techniques. You can see the article here: https://doi.org/10.1016/j.jqsrt.2017.07.010
We measured absolute frequency of the unperturbed P7 P7 O2 B-band transition 434783.5084857(82) GHz and the collisional self-shift coefficient GHz/(molecule/cm3). With Doppler-limited spectroscopy we achieved the relative standard uncertainty of on line position, typical for Doppler-free techniques. Shapes of the spectral line were measured with a Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer referenced to an 88Sr optical atomic clock via an optical frequency comb.