Ames-2021 CO Dipole Moment Surface and IR Line Lists: Toward 0.1% Uncertainty for CO IR Intensities.

A highly accurate CO dipole moment surface (DMS), Ames-2021, is reported along with CO infrared (IR) intensity comparisons approaching a 1-4‰ level of agreement and uncertainty. The Ames-2021 DMS was accurately fitted from CCSD(T) finite-field dipoles computed with the aug-cc-pVXZ (X = T, Q, 5) basis for C atom and the d-aug-cc-pVXZ (X = T, Q, 5) basis for O atoms, and extrapolated to the one particle basis set limit. Fitting σ is 3.8 × 10 au for 4443 geometries below 15 000 cm. The corresponding IR intensity, , are computed using the Ames-2 potential energy surface (PES), which is the best PES available for CO. Compared to high accuracy IR studies for 2001-00001 and 3001-00001 bands, matches NIST experiment-based intensities [ or ] to -1.0 ± 1.3‰, or matches DLR experiment-based intensities [] to 1.9 ± 3.7‰. This indicates the systematic deviations and uncertainties have been significantly reduced in . The (or ) have larger deviations (vs ) and uncertainties (vs , ) which are attributed to the less accurate Ames-1 PES adopted in UCL-296 line list calculation. The intensity of CO and CO is utilized to derive new absolute C/C ratios for Vienna PeeDee Belemnite (VPDB) with uncertainty reduced by / or /. Further evaluation of intensities are carried out on those CO bands discussed in the HITRAN2020 update paper. Consistent improvements and better accuracies are found in band-by-band analysis, except for those bands strongly affected by Coriolis couplings, or very weak bands measured with relatively larger experimental uncertainties. The Ames-2021 296 K IR line lists are generated for 13 CO isotopologues, with 18 000 cm and > 1 × 10 cm/molecule cutoff and then combined with CDSD line positions (except CO). The Ames-2021 DMS and 296 K IR line lists represent a major improvement over previous CO theoretical IR intensity studies, including Ames-2016, UCL-296, and recent UCL DMS 2021 update. A real 1 permille level of agreement and uncertainty will definitely require more accurate PES more accurate DMS.