CO transition frequencies with kHz-accuracy by saturation spectroscopy in the 1.99-2.09 μm region

• Published in: Physical chemistry chemical physics : PCCP 2023-06, Vol.25 (24), p.16319-1633
• Main Authors: Fleurbaey, H, ermák, P, Campargue, A, Kassi, S, Romanini, D, Votava, O, Mondelain, D
• Format: Article
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/d3cp01603j

Saturation spectroscopy has been used to determine the absolute frequencies of 107 ro-vibrational transitions of the two strongest 12 CO 2 bands of the 2 μm region. The considered 20012-00001 and 20013-00001 bands are of importance for the CO 2 monitoring in our atmosphere. Lamb dips were measured using a cavity ring-down spectrometer linked to an optical frequency comb referenced to a GPS-disciplined Rb oscillator or to an ultra-stable optical frequency. The comb-coherence transfer (CCT) technique was applied to obtain a RF tunable narrow-line comb-disciplined laser source using an external cavity diode laser and a simple electro-optic modulator. This setup allows obtaining transition frequency measurements with kHz-level accuracy. The resulting accurate values of the energy levels of the 20012 and 20013 vibrational states are reproduced with a (1 σ )-rms of about 1 kHz using the standard polynomial model. The two upper vibrational states appear thus to be highly isolated except for a local perturbation of the 20012 state leading to an energy shift of 15 kHz at J = 43. A recommended list of 145 transition frequencies with kHz accuracy is obtained providing secondary frequency standards across the 1.99-2.09 μm range. The reported frequencies will be valuable to constrain the zero-pressure frequencies of the considered transitions in 12 CO 2 retrieval from atmospheric spectra. Saturation spectroscopy is used to provide absolute frequencies of 145 transitions of 12 CO 2 with kHz accuracy in the 2 μm region.