Application of perturbation theory to coupled Morse oscillators

We apply perturbation theory by the moment method to two-dimensional anharm onic oscillators that exhibit non-degenerate and strongly mixed near-degene rate unperturbed states. Simple recurrence relations give the perturbation corrections to the energy and moments of the selected state. We explicitly consider the vibrational energy levels of coupled Morse oscillators, parame trized for the two stretching modes SO2 and H2O, and discuss the applicatio n of the method to more general problems. (C) 1999 Elsevier Science B.V. Al l rights reserved.