Role of molecular symmetry and molecular interactions in the Faraday effect of fluids

Abstract

General expressions are developed for assessing the effects of molecular symmetry and molecular interactions on the rotation of plane polarized light in the presence of a static magnetic field. This is accomplished by writing the Verdet constant V as a sum of four terms : V = VD O + VPO + VDINT + VPINT where the subscripts 0 and INT refer, respectively, to the absence and presence of molecular interactions in the presence of the external magnetic field and the superscripts D and P denote, respectively, diamagnetic and paramagnetic contributions. The results, which are given in terms of c- and i-tensors and radial and radial-angular correlation functions, are analyzed in terms of magnetic point group symmetries and applied to rarefied and dense systems. From the experimental Verdet constants at atmospheric pressure we calculate the mean electromagnetic hyperpolarizability tensor α* 123(ω) for the molecules He, H2, N2, Cl 2, CO2, HCl, CO, NH3 and CH4. We also calculate α*123(ω) for liquid CS2 and C 6H6 and the contribution due to nearest neighbour interaction to the Verdet constant It is found that VDINT/ VDO = 22.8 % for CS2 and 8.4 % for C 6H6. We also list, for all magnetic point groups, the tensors which describe the Faraday effect.