High Sensitivity CW-CRDS Spectroscopy of the Eight Most Abundant CO2 isotopologues between 5851 and 7045 cm_1 . Critical Review of the Current Databases

The exhaustive line positions analysis of the absorption spectrum of carbon dioxide in natural abundance has been performed on the basis of high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 7045 cm_1 (1.71-1.42 µm). The achieved sensitivity (noise equivalent absorption _min _ 2_5_10_10 cm_1 ) combined with the high linearity and dynamics (more than 4 decades) of the CW-CRDS technique, have allowed the detection of 8293 transitions of the 12C 16O2, 16O12C 17O and 16O12C 18O isotopologues. They belong to a total of 130 bands. Line intensities of the weakest transitions are on the order of 2_10_29 cm_1/(molecule cm_2 ). The rovibrational assignments were performed on the basis of accurate predictions of the effective Hamiltonian model of the respective isotopologues. The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 121 bands from a fit of the measured line positions. A number of resonance interactions were identified. In particular, the first observation of an interpolyad coupling is reported for the 16O12C 18O isotopologue. A similar experimental database has been constructed for the 13C 16O2, 16O13C 18O, 16O13C 17O, 13C 18O2 and 17O13C 18O isotopologues of carbon dioxide on the basis of CWCRDS spectra of carbon dioxide with 99 % enrichment in 13C. A total of 8639 transitions of the five 13C isotopologues were assigned. They belong to a total of 150 bands while less than 20 bands were previously reported by Fourier Transform spectroscopy in the region. Accurate line intensities of 2039 transitions ranging between 1.1_10_28 and 1.3_10_23 cm_1/(molecule cm_2 ) were used together with FTS data to determine the effective dipole moment parameters in the frame of the effective operators approach. A list of 13C 8639 transitions has been constructed: line positions are experimental values (typical uncertainty on the order of 1_10_3 cm_1 ) while line strengths were calculated at 296 K by using the effective operators approach (typical uncertainty on the order of 5 %). In the case of the 13C 16O2 isotopologue, the reported transitions represent 99.65 % of the total absorbance in the region considered. The obtained experimental datasets which are the most complete in the considered region, have been used for a critical
review of the most currently used spectroscopic databases of carbon dioxide: HITRAN, GEISA, HITEMP, and the recent JPL and CDSD databases.