Semi-empirical dipole moment of carbon monoxide and line lists for all its isotopologues revisited

The semi-empirical permanent electric dipole-moment function (DMF) for the ground state of the CO molecule has been reconstructed analytically in the entire range of the inter-nuclear distance r ∈ [ 0 , + ∞) by means of the simultaneous non-linear least-squares fitting (NLLSF) of the selected experimental intensities for the main 12C^{16O isotopologue (including those with sub-percent uncertainties) and the ab initio permanent dipole moment. The ab initio DMFs were evaluated using single-reference coupled cluster (SR-CCSD(T)) and multi-reference averaged coupled-pair functional (MR-ACPF) methods. The ab initio data were involved in the NLLSF procedure to propagating smoothly the semi-empirical DMF outside the local region covered by the experimental intensities for the lowest vibrational v' ≤ 11 levels. The derived mass-invariant DMF possesses the physically correct asymptotic behavior in both the united-atom and dissociation limits as well as reproduces the vast majority of the measured intensities in v″ = 0 →v' ∈ [ 0 , 6 ] and v″ = 1 →v' = 4 , 5 bands within their experimental uncertainties. The resulting DMF and the mass-corrected potential-energy function of Meshkov et al. (2018)[16] were used to upgrade line lists for all CO isotopologues in the wide range of vibrational and rotational quantum numbers v ∈ [ 0 , 41 ] , Δ v ∈ [ 0 , 6 ] , J ∈ [ 0 , 150 ] (J ∈ [ 0 , 200 ] for the 0-0 and 1-0 bands). The predicted intensities are compared with their experimental counterparts, which were not involved in the present NLLSF, to highlight presumable random and systematic errors in the measured data; in particular, the intensities in the "abnormal" 0 → 5 band of the 12}C^{16O isotopologue and some other bands of minor isotopologues should be revisited experimentally. The resultant line list should be considered superior to previous efforts in terms of accuracy.}