General anharmonic local mode approach to molecular vibrations

An algebraic approach to describe the vibrational excitations of molecules is presented. The model is established in a local mode scheme and involves an anharmonization procedure in which the local,harmonic oscillators associated to each internal degree of freedom are substituted by Morse oscillators through the introduction of U(2) algebras. This anharmonization corresponds exactly to the dominant Morse matrix elements involved in the harmonically coupled anharmonic oscillator (HCAO) model introduced by Child and Lawton. An application to methane is presented. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 465-481, 1999.