Valence states and a universal potential energy curve for covalent and ionic bonds

The relations between the diatomic spectroscopic constants and a novel parameter DVS, the valence state dissociation energy, are investigated. An energy scaling by DVS, instead of the spectroscopic De, allows the formulation of a universal three-parameter valence state potential energy curve (VS-PEC). The second and higher derivatives at the equilibrium distance, Re, are simple functions of a valence state parameter z = keRe2/DVS. The analysis of the VS-PECs of 25 single and multiple bonded molecules covering the whole range of polarity reveals a far greater similarity near the minimum than previously reported. In comparison with the Morse and Rydberg potentials, the accuracy of the calculated vibration-rotation coupling and anharmonicity constants is improved by an order of magnitude.