Molecular transition frequencies of CO2 near 1.6 μm with kHz-level uncertainties

We present measurements of molecular transition frequencies based on the comb-locked cavity ring-down spectroscopy technique, reporting vacuum transition frequencies of Doppler-broadened (CO2)-C-12-O-16 in the 1.6 mu m region for the (30012) <- (00001) and (30013) <- (00001) bands with an average combined standard uncertainty of approximate to 1 kHz. A global four-state model was fit to these data and literature values to provide spectroscopic parameters and a best-case fit precision of 4 kHz. We identified and quantified an interaction between the (30012) and (33301) states which was manifest as an observed Fermi-resonance-type perturbation in the (30012) <- (00001) band. This interaction was accounted for in the global fit, substantially reducing systematic uncertainties in the spectroscopic parameters of the (30012) state and altering many predicted transition frequencies in the (30012) <- (00001) band by 1 MHz or more relative to literature values. The accurate transition frequencies reported here may be considered as SI-traceable reference data for diverse applications including remote sensing and telecommunications. Published by Elsevier Ltd.

Automated summary

The study presents measurements of molecular transition frequencies using comb-locked cavity ring-down spectroscopy technique, reporting vacuum transition frequencies of Doppler-broadened (CO2)-C-12-O-16 with high accuracy. A global four-state model was fitted to the data with a precision of 4 kHz. Moreover, an interaction between (30012) and (33301) states was identified and quantified, which was accounted for in the global fit.