An extended SU(2) model for coupled Morse oscillators

The SU(2) vibron model has been shown to correspond to an approximation whe re only the dominant Delta upsilon = ii interaction between Morse oscillato rs is taken into account [A. Frank, R. Lemus, M. Carvajal, C. Jung, E. Ziem niak, Chem. Phys, Lett, 308 (1999) 91]. We extend the algebraic model in or der to incorporate higher-order couplings for the Morse oscillators, thus, providing a means to establish an exact quantum-mechanical connection with traditional phase-space descriptions of molecular vibrations. Results for t he energy spectrum for two coupled Morse oscillators are compared with both the traditional and extended SU(2) models, as well as with the Child-Lawto n model. The wave functions corresponding to the different models are also examined. A classical analysis is carried out in order to further explore t he interrelations between these models. (C) 2000 Elsevier Science B.V. All rights reserved.