Application of perturbation theory to the vibration-rotational energies of diatomic molecules

Abstract

To determine the vibration-rotational energies of diatomic molecules, the hypervirial perturbation theory is proved to be simpler and more convenient than other approaches. The expansion of these energies in terms of a small parameter related to the spectral parameters is independent of the unperturbed model chosen. They illustrate this point by the selection of the harmonic oscillator and the Morse oscillator as two possible unperturbed models. They apply the hypervirial perturbative method to a modified Morse oscillator, proposed earlier to analyse the spectra of diatomic molecules, for which obtain the energy coefficients in terms of the parameters of the potential-energy function.