Description of diatomic molecules using one electron configuration energies with two-body interactions

Abstract

It has recently been shown that the vibrational potential energy for a diatomic molecule α‐β may be written exactly in the form (i) W(R) = W_β(R)+W_NPF(R), where W_β(R) is the electrostatic interaction energy between nucleus α and the free atom β and W_NPF(R) is the electrostatic interaction energy between nucleus α and the ``Non‐Perfectly‐Following'' electronic charge density redistributions arising when atoms α and β form the molecule α‐β with the internuclear distance R. In this paper it is shown that W_NPF(R) may be approximated, within a constant near equilibrium, by the extended Hückel configuration energy, taken as a simple sum of orbital energies, W_EH(R), yielding an approximate molecular energy W*(R) according to the formula (ii) W*(R) = W_β+W_EH(R). Comparisons are made between W*(R) and the experimental W(R) for first and second period diatomic molecules. Equation (ii) overcomes the deficiency present when either W_β(R) or W_EH(R) alone is used to estimate equilibrium internuclear distances, although equilibrium force constants may be derived from W_β(R) if the equilibrium distances are known.