APPLICATION OF THE HYPERVIRIAL PERTURBATION-THEORY TO THE VIBRATIONAL-ROTATIONAL SPECTROSCOPY OF DIATOMIC-MOLECULES

We have developed a simple and systematic method to calculate analytic perturbation corrections of large order to the vibrational-rotational energies and matrix elements between vibrational-rotational states of diatomic molecules. The method, which is based on a powerful combination of perturbation theory and the hypervirial and Hellmann-Feynman theorems, is suitable to derive analytic expressions for both expectation values of observables and transition moments. As an illustrative example we discuss the isotopic effect on the vibrational-rotational energies. We show that, according to the Kratzer potential-energy function, perturbation theory renders a good approximation to the vibrational-rotational energies of diatomic molecules. © 1990 The American Physical Society.