Magneto-chiral birefringence and dichroism

Abstract

It was pointed out recently that the absorption coefficient of a chiral molecule should be shifted slightly in a magnetic field parallel to a light beam in any polarization state. This suggestion is developed further by considering an analogous refractive index shift and by discussing these magneto-chiral phenomena in the unified context of effects generated by the ‘magnetic’ (time-odd) parts of the complex optical activity tensors. Explicit expressions, in terms of molecular property tensors, are derived for the difference in refractive index and absorption coefficient of a chiral molecule in a magnetic field parallel and antiparallel to the light beam, and magneto-chiral analogues of the Faraday A-, B- and C-terms introduced. A rough estimate of the magneto-chiral birefringence indicates that it should be observable using a modified Rayleigh refractometer. The feasibility of observing magneto-chiral dichroism A-, B- and C-terms in different types of chiral molecules is also considered. The magneto-chiral observables are shown to transform as time-odd polar vectors.