Optical Anisotropy of Chain Molecules. Theory of Depolarization of Scattered Light with Application to n-Alkanes

Abstract

Depolarization of light scattered by chain molecules is treated according to the valence‐optical scheme which rests on the assumption that the polarizabilitytensor α for the molecule may be formulated as the sum of contributions of individual bonds, or of constituent groups. The anisotropy of the polarizability is described by the tensor invariant γ2 (proportional to the sum of the squares of the elements of the traceless part of α), which determines the depolarization ratio. This invariant (γ2) is averaged over all configurations of the chain molecule treated in the rotational isomeric‐state approximation, interdependence of rotations about neighboring bonds being taken into account. Beyond the stated assumptions, the treatment is exact; it is applicable to chains of any length, and of any specified structure. Illustrative calculations for the n‐alkanes are presented and compared with experimental depolarization results for liquids of this homologous series and for their solutions in solvents of low optical anisotropy.