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

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 = VDO + 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 cand 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 03B1*123(03C9) for the molecules He, H2, N2, Cl2, CO2, HCl, CO, NH3 and CH4. We also calculate 03B1*123(03C9) for liquid CS2 and C6H6 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 C6H6. We also list, for all magnetic point groups, the tensors which describe the Faraday effect. J. Physique 44 (1983) 403-410 MARS 1983, Classification Physics Abstracts 34.90 35.20M 78.20L 1. IntroductiorL Studies of optical effects in gases and liquids exposed to external electric or magnetic fields increase our knowledge of molecular properties (*) Supported in part by a grant from the National Institutes of Health, GM23223. Supported in part by the Polish Academy of Sciences (Research Project MR. I . 9). (**) Permanent address : Nonlinear Optics Division, Institute of Physics, A. Mickiewicz University, 60-78 Poznan, Poland. and intermolecular correlations. Faraday [1] discovered that a static magnetic field B°, acting on a medium in which a linearly polarized beam of monochromatic light propagates in the direction of B°, rotates the light polarization plane. A quantummechanical theory of the Faraday effect was first proposed by Kronig [2], for diatomic diamagnetic molecules, and subsequently extended to atoms by Carrol [3] and Rosenfeld [4], to one-electron systems in the realistic approximation by Kroll [5], and the Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphys:01983004403040300