Light scattering studies of orientational pair correlations in liquids composed of anisometric molecules

Abstract

The nature of the intermolecular forces which are important in determining the magnitude of orientational pair correlations (OPC) in liquids is studied by combining high pressure and depolarized Rayleigh light scattering techniques. For molecules of similar shape (toluene, bromobenzene, and nitrobenzene) we find that the magnitude of the OPC as measured by depolarized light scattering is not simply a function of the packing of the molecules. For 16 monosubstituted derivatives of benzene, we find that the magnitude of the OPC correlates well with the square of the molecular dipole moment. This correlation of OPC with dipole moment is understood by relating both the molecular dipole moment and the magnitude of the OPC to the detailed distribution of molecular electronic charge. The light scattering reorientational relaxation times for toluene, bromobenzene, and nitrobenzene as a function of pressure have also been measured and found to be linear functions of viscosity.