Symmetry restrictions for natural and induced circular dichroism and optical activity for all point groups

Abstract

Group theoretical techniques are used to analyse the geometrical dependence of natural circular dichroism (CD) and circular dichroism induced by a linear interaction with either a magnetic (MCD) or electric field (ECD). For each of these effects the dependence of the spectra on the relative orientations of the crystal, radiation, and the external field, is given for each point group. At arbitrary orientations the spectrum is a linear superposition of a definite number of irreducible spectra. For example, MCD has axial symmetry in the groups Dn, Dnb, Cnv(n not=2), D2d, D3d while ECD is always forbidden in cubic symmetry, and also for non-cyclic groups if the field and radiation are parallel. The results apply equally to the analogous transmission effects, i.e. natural optical activity, electro-optical activity and the magnetic-field-induced Faraday effect.