The dipolar correlation factor and dipole moment of a water molecule in ice III

The dipolar correlation factor, g, of polycrystalline ice III (completely proton-disordered ice IX) has been calculated using the molecular data for its crystal structure. For dendritic probabilities of orientation of water molecules, the contribution to g from the first, second and third neighbours is 1.232, 0.165 and 0.016, respectively, g is 2.414 and the average dipole moment of a water molecule in ice III is 2.55 D. This agrees with the value 2.45 D calculated from Onsager's model of a point dipole at the centre of a spherical cavity of isotropic polarizability expressed by optical permittivity. g has been calculated also from the literature data obtained from X-ray diffraction of quenched ice III assuming it to be completely proton-disordered. The value is 2.396. The result indicates the insensitivity of g to the molecular constants within the same unit cell of a crystal.