Anharmonic Algebraic Model of Thermodynamic Properties of Diatomic Molecules

An algebraic model based on Lie-algebraic techniques is applied to the analysis of thermodynamic vibrational properties of diatomic molecules. The local anharmonic effects are described by a Morse-like potential and corresponding anharmonic bosons associated with the U(2) algebra. A vibrational high temperature partition function and the related thermodynamic functions are derived in terms of the parameters of the model. The thermal expansion operator is defined and obtained using the renormalized frequency of the model. 1. Anharmonic Algebraic Model Algebraic models have been used very successfully in nuclear physics and have led to new insights into the nature of complex many body systems [1]. Similar methods have been proposed to describe molecular excitations [2,3]. The methods combine Lie algebraic techniques, describing the interatomic interactions, with discrete symmetry techniques associated with the molecules. In the framework of the algebraic model [2], the anharmonic effects of the local interactions are described by substituting the local harmonic potentials by Morse-like potential, associated with the U(2) algebra. The one-dimensional Morse Hamiltonian is written in terms of the generators of U(2),