On the theory of the alignment of a polar molecule in a non-polar solvent

The alignment average of a dilute polar substance dissolved in a non-polar solvent may be derived from the NMR spectrum of the polar component. Likewise, the Kerr effect is related to this quantity.In this paper a series expansion of the alignment of a polar molecule in a non-polar solvent is presented for a rigid-lattice model, first introduced by Van Vleck for the dielectric constant of a very dilute solution. Different results up to second order in the dipolar interaction are obtained for a simple, a body centred, or a face centred cubic lattice and a lattice whose lattice points are uniformly distributed in a continuum. The latter formula is compared with that calculated on the basis of the Lorentz local field model and with that of Buckingham in which the interaction between the dipoles themselves is neglected.