Second Virial Coefficients of Polar Gases

An equation is given for the classical second virial coefficient of a polar gas in terms of the parameters appearing in an intermolecular potential energy which includes London and dipole attraction and inverse-power repulsion. The equation is successfully fitted to the data for H2O and NH3 with allowance for the small quantum correction, and the derived values of the London constant are in good accord with theoretical estimates. The defects of the model and its relation to the concept of the hydrogen bond are briefly discussed.