On the direct determination of analytical diatomic potential energy functions from spectroscopic data: the X ¹∑⁺ electronic states of NaF, LiI, CS, and SiS

Line positions available in the literature for vibrational-rotational and pure rotational transitions have been employed to determine accurate effective potential energy curves for the ground electronic states of ²³Na¹⁹F and ⁷Li¹²⁷I, and Born-Oppenheimer potentials and associated radial functions describing Born-Oppenheimer breakdown corrections for CS and SiS. In each case, a small number of fitted parameters represents the entire data to within the measurement accuracies. Rotational and centrifugal distortion constants are calculated a posteriori through perturbation theory. For SiS, the results are compared with those of a recent analysis by Ogilvie, and it is found that eigenvalues calculated by numerical solution of the radial equation with effective Hamiltonians defined by the present results are greatly improved over those calculated from Hamiltonians defined by Ogilvie's parameters.