The nonrigid bender Hamiltonian using an alternative perturbation technique

Abstract

Abstract The derivation of the nonrigid bender Hamiltonian for the calculation of the rotation-vibration energies of a triatomic molecule was completed by P. Jensen and P. R. Bunker [J. Mol. Spectrosc. 99, 348–356 (1983)] using Van Vleck perturbation theory. This perturbation technique assumes that the bending vibration frequency is much less than the stretching vibration frequencies (such as in the ground electronic state of C3). For molecules such as H2O, for which this is not the case, an alternative formulation of the theory is possible in which allowance is made for the dependence of the perturbation theory energy denominators on the bending vibration quantum number v2 and on the rotational quantum number K. This was pointed out by A. R. Hoy and P. R. Bunker [J. Mol. Spectrosc. 74, 1–8 (1979)], and some of the corrections were made by them. We now develop the perturbation theory expressions allowing for the dependence of all the energy denominators on v2 and K.