A thermodynamic method of estimating anharmonic molecular densities of states

Simple relations between the experimentally observable thermodynamic proper ties and the molecular density of states ate utilized to provide a method o f accurate evaluation of the vibrational density of states taking into acco unt both quantum and anharmonic effects. The result is a smooth function of energy that represents a local average of the exact density of states. Alt ernatively, it is shown that the anharmonic vibrational density of states m ay, at least for the small molecules NO2, HO2 and H2O, be obtained from inf ormation on the normal mode frequencies and bond energies if one represents the molecule as a set of uncoupled Morse and harmonic oscillator, where th e Morse oscillators correspond to the stretching vibrations.