Application of Drude term in the interpretation of crystalline optical activity

The possibility of applying the Drude term in the interpretation of the optical rotatory dispersion of crystals with the optical activity of a crystalline origin is presented. Using the perturbation theory the presence of the Drude term in the optical rotatory dispersion relations derived for the modified models of coupled oscillators is proved. Necessary conditions define this Drude term application, i.e. for its use in the description of the optical rotatory dispersion of crystals consisting of the optically inactive particles. The presented theory is considered as the second limit in the calculation of the oscillator strengths of the normal modes of vibrations in comparison with the classical approach to them. The presented results are of use in the case of the α-quartz, whereas the application of the Drude term in the optical rotatory dispersion relations for tellurium crystal does not improve substantially the interpretation of the experimental data.