New CW-CRDS measurements and global modeling of 12C 16O 2 absolute line intensities in the 1.6 μm region

Abstract

Line intensities of 12C 16O 2 transitions have been measured by CW-Cavity Ring Down Spectroscopy in four wavenumber intervals near 1.6 μm. Intensity values of 952 transitions ranging from 1.10 × 10 −28 to 4.94 × 10 −25 cm/molecule were retrieved with an average accuracy of 4%. These transitions belong to a total of 30 bands corresponding to the Δ P = 9 series of transitions. The achieved sensitivity (noise equivalent absorption α min ∼ 3 × 10 −10 cm −1) allows lowering by more than two orders of magnitude the lower intensity values measured in the region. Comparison with the values included in the JPL database [R.A. Toth, L.R. Brown, C.E. Miller, V. Malathi Devi, D.C. Benner, J. Quant. Spectrosc. Radiat. Transf. 109 (2008) 906–921] shows residuals exceeding one order of magnitude for weak lines. The measured intensities together with a selection of experimental intensities available in the literature were used to extend and refine the set of effective dipole moment parameters for the Δ P = 9 series of transitions of the principal isotopologue of carbon dioxide. The refined parameters allow reproducing, within the experimental uncertainties, the whole set of intensity measurements which extends over nearly six orders of magnitude (1.10 × 10 −28–6.12 × 10 −23 cm/molecule). Combining the CW-CRDS line positions with the calculated line intensities, a line list has been generated for the whole 5851–7045 cm −1 region and is provided as Supplementary Material. The obtained effective dipole moment parameters have also been used to generate the Δ P = 9 series of transitions included in the new version of the CDSD database. The comparison of the CDSD line intensities with the values provided by the HITRAN-2004 database shows discrepancies up to 80% for some of the bands while discrepancies up to three orders of magnitude are noted for the weakest bands included in the JPL database.