  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.
