High sensitivity CW-Cavity Ring Down Spectroscopy of five 13CO2 isotopologues of carbon dioxide in the 1.26-1.44 μm region (I): Line positions

The absorption spectrum of highly enriched 13C carbon dioxide has been investigated by CW-Cavity Ring Down Spectroscopy with a setup based on fibered distributed feedback (DFB) laser diodes. By using a series of 30 DFB lasers, the CO2 spectrum was recorded in the 7029-7917 cm−1 region with a typical sensitivity of 3×10−10 cm−1. The uncertainty on the determined line positions is on the order of 8×10−4 cm−1. More than 3800 transitions with intensities as low as 1×10−29 cm/molecule were detected and assigned to the 13C16O2, 16O13C17O, 16O13C18O, 17O13C18O and 13C18O2 isotopologues. For comparison, only 104 line positions of 13C16O2 were previously reported in the literature in the considered region. The band-by-band analysis has led to the determination of the rovibrational parameters of a total of 83 bands including 56 bands of the 13C16O2 species. The measured line positions of 13C16O2 and 16O13C18O were found in good agreement with the predictions of the respective effective Hamiltonian (EH) models but the agreement degrades for the minor isotopologues. Several cases of resonance interactions were found and discussed. In the 20033-10002 band of 13C16O2, an anharmonic resonance interaction leads to deviations on the order of 0.05 cm−1 compared to the EH predictions. The existence of interpolyad interactions affecting the non-symmetric isotopologues of carbon dioxide is confirmed by the observation of two occurrences in 16O13C17O and 16O13C18O. The obtained results improve significantly the knowledge of the spectroscopy of the 13C isotopologues of carbon dioxide. They will be valuable to refine the sets of effective Hamiltonian parameters used to generate the CDSD database.