The ground electronic state of CS: A global multi-isotopologue direct potential fit analysis

A collection of 6759 pure-rotational and vibrational–rotational spectroscopic line positions available for seven isotopologues of the ground X¹Σ⁺ electronic state of carbon monosulfide has been employed in a weighted nonlinear least-squares direct fit to the potential energy function of ¹²C³²S and supplementary functions describing breakdown of the Born-Oppenheimer approximation. All radial functions are represented by compact analytical models having proper theoretical asymptotic behavior. The spectroscopic line positions are reproduced on average to within the associated experimental uncertainties by the quantum–mechanical eigenvalues of the derived Hamiltonians for individual isotopologues. The potential energy function is constrained to obey the theoretical radial behavior both at short-range and at long-range. Accurate quantum–mechanical vibrational term values and rotational and centrifugal distortion constants are provided for all stable isotopologues of CS included in the least-squares fits.