Abstract
The formulae for the application of thermodynamic perturbation theory to an octahedral molecule whose first permanent electric multipole is a hexacapole have been developed. They are applied to the prediction of the thermodynamic properties of sulphur hexafluoride from a spherical (n - 6) reference potential. A comparison between experimental data and the predictions for sulphur hexa-fluoride show that the theory is of sufficient accuracy for many engineering purposes although it is unable to reproduce the entire set of experimental information within its estimated uncertainty.