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In this paper we generalize the quantum mechanical model of three coupled oscillators because of its usage in the crystal optical activity. Using this model we can include the influence of all essential couplings between single oscillators which represent the molecules or atoms of optically active crystals belonging for example to the space groups of symmetry D 4 3 or D 6 3 . The single oscillators are damped and therefore we can include both parts of the optical activity -optical rotatory dispersion and circular dichroism -into computations. We present more universal formulas for description of the above mentioned parts.

The three coupled oscillator model and its application to the explanation of opticalrotatory dispersion and circular dichroism of benzil crystal is discussed. The previously measured experimental data are approximated by the theoretical set of formulas provided by this model. The twelve-term formula, which was computed using our computer program, is derived from the interpretation of the opticalrotatory dispersion of benzil. Similarly, the circular-dichroism data are analyzed. Both the previously published experimental data and the latest measurements are used for this reason. The obtained results are compared and discussed with respect to the origin of the optical activity occurring in benzil crystal.

An interpretation of the most recent experimental data on the optical rotatory dispersion of tellurium is presented. The experimental data are approximated by theoretical equations which were derived using the model of three coupled oscillators. The applied mathematical method is based on the sum of least squares. The derived equations are also helpful when modelling the circular dichroism of tellurium and discussing the sense of the rotation of the linear polarized light with regard to the crystal structure.

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