Cavity ring-down spectroscopy of CO2 near λ = 2.06 µm: Accurate transition intensities for the Orbiting Carbon Observatory-2 (OCO-2) “strong band”

The update of the line positions and intensities in the line list of carbon dioxide for the HITRAN2020 spectroscopic database

“…In Fleurbaey et al [20], it was shown that a constant scaling of 1.0069±0.0002 of HITRAN2016 values in the 20013-00001 band of CO2 near 2.06 μm is consistent with the experiment. Therefore, we have performed this scaling in HITRAN2020.…”

“…In particular, the accurate values of the line intensities with uncertainties as low as 0.3%-0.5% [49] are necessary for forward models used in retrievals of CO2 concentrations from some remote sensing missions. A number of very accurate measurements have become available after the release of HITRAN2016 in the NIR region: the most recent CRDS measurements from NIST [19,20] and FTS measurements from DLR reported in Birk et al [22] (with the corresponding measurements and line parameter database provided on Zenodo [21]).…”

“…For wavenumbers below 8000 cm -1 , we discuss line intensity updates to the HITRAN2016 line list for bands provided by the Carbon Dioxide Spectroscopic Databank (CDSD) based on global fits of semi-empirical models to measurements and those obtained by the ab initio calculations of University College London (UCL). In Section 4, we discuss new measurements with sub-percent relative uncertainty [19][20][21][22] that were used to improve some CO2 bands in the 1.4 to 2.1-µm region. In Section 5, we present new CO2 bands above 8000 cm -1 that have been included in the HITRAN2020 edition from the latest high-temperature line list of the ExoMol [18] database (with appropriate cut-off) for the main CO2 isotopologue and the CRDS spectra [14] for the 16 O 12 C 18 O isotopologue.…”

Absolute 13C/12C isotope amount ratio for Vienna PeeDee Belemnite from infrared absorption spectroscopy

“…Temperature stabilization was enhanced using an insulating box around the AIR-IS sample cell and was monitored during spectral acquisition using calibrated platinum resistance thermometers in good thermal contact with the outside of the enhancement cavity. A comprehensive summary of the NIST technical approach to accurate gas metrology by CRDS can be found in Fleurbaey et al 33 .…”

“…To evaluate uncertainty in the predicted 13 C 16 O 2 transition intensities, we also calculated transition intensities for 12 C 16 O 2 and compared with highly accurate experiments 33,[47][48][49] . For ground-state rotational quantum numbers of J″ = 12 and J″ = 18 we find that, for five near-infrared vibrational bands of 12 C 16 O 2 , the standard deviation of a uniform distribution chosen to represent the experimental measurements relative to the predictions of our updated ab initio DMS is equal to 3.8 × 10 −3 .…”