Dispersion models exhibiting natural optical activity: application to tartaric acid solutions

Abstract

A physically consistent dispersion model, incorporating the optical activity of an isotropic medium and dependent on the size and direction of the wave vector, is presented and used in the optical characterization of a solution of tartaric acid in dimethyl sulfoxide. It is shown that the optical activity can be described simply by three optically active harmonic oscillators. Two of these oscillators effectively describe the excitation of valence electrons, while the third describes the excitation of vibrational states in tartaric acid molecules. Higher-energy valence electron excitations are identified as the bond energies of C-C bonds, and lower-energy excitations correspond to the remaining bonds. The results presented in this work are compared with the results that can be obtained using the phenomenological models commonly used in practice. As part of the optical characterization, the non-locality radius of the dielectric response was found to be surprisingly large, namely, 56 nm.