In this paper the Raman vibrational spectra for all actually realized geometries of and crystals at 77 K, and infrared reflectivity spectra for both and polarizations in the range from 50 to at 300 K have been investigated. The contours of the reflectivity spectra are calculated by means of the classical dispersion relations of the multi-oscillator model, and the fundamental phonon parameters and the static and high-frequency dielectric constants are determined as well. Davydov multiplet vibrational modes have been revealed in both crystals.

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The study of both the absorption and λ-modulated absorption spectra have been investigated in the region of the lowest band gap. The reflectivity spectra of ZrS2 are presented in the region E>E g (1.5 to 6.5 eV). The IR reflectivity spectra of ZrS2 for E⊥c polarization were investigated in the region from 50 to 4000 cm-1. The contours of vibrational spectra were calculated using multioscillator model and the parameters of phonons were determined. New data about the band structure were obtained in the region of the lowest band gap.

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The Raman scattering and IR reflectivity have been investigated for different crystal configurations. The contours of reflectivity spectra have been calculated. The angle dependence of polar vibrational modes in both reflectivity and Raman spectra have been investigated. The peculliarities of the transition from longitudinal mode to transverse one and vice versa both with and without changing of symmetry have been obtained. The phonon parameters and effective ionic charges of the anions and cations have been determined. It has been shown that there exists an effective ionic charge anisotropy of the oxygen and tellurium ions. ExperimentalMonocrystal, obtained by the Czochralski method, were cut in plateshape (2 x 1 cm) and cubic (0.5 x 0.5 x 0.5 cm) samples. We investigated Raman scattering by using a DFS-32 spectrometer