The Effect of Rotational Distortion on the Thermodynamic Properties of Water and Other Polyatomic Molecules

摘要

The classical mechanical expression for the energy of a nonhyphen;vibrating, rotating polyatomic molecule is obtained which includes a correction term arising from the centrifugal distortion of the molecule caused by the rotation. Since the rotational partition function closely approaches the classical phase integral for room temperatures or higher, the latter is used to calculate the effect of centrifugal distortion on the entropy, heat capacity and free energy. The correction terms mdash;rgr;RT2, 2rgr;RTand 2rgr;RTmust be added toF, SandCv, respectively. rgr; is a constant characteristic of each molecule. The values of rgr; calculated are: H2O, 2.04 10mdash;5; H2S, 1.62 10mdash;5; NH3, 1.45 10mdash;5; CH4, 1.72 10mdash;5; C2H4, 0.79 times; 10mdash;5. For water this correction amounts to approximately frac12; percent of the heat capacity at the boiling point, or +0.032 entropy unit.