CHARACTERIZATION OF VIBRATIONAL TRANSITION MODES BY USE OF NORMAL FORMS

In this paper we use the Birkhoff-Gustavson perturbation theory to ana lyze the vibrational modes of two linearly coupled Morse oscillators i n the transition region from normal modes to local modes. Our study is based on: truncation of the Hamiltonian written in normal mode coordi nates at the 4th order, transformation to normal form and analytical s tudy; construction and use of the approximate integrals of motion of t he exact Hamiltonian according to Birkhoff and Gustavson theory. By co mparison with a previous analytical study, we demonstrate that perturb ation theory, based either on local or normal modes can be used to acc urately describe transition modes.