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

Abstract

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 12C16O 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],Δv∈[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 12C16O 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.