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The Raman scattering of MOO, at 300 and 77 K and the infrared reflectivity spectra of MOO, at 300 K have been investigated in different scattering geometries. The Raman spectra of PbMoO, crystals at 77 K have been investigated also. The reflectivity spectra of MOO, crystals were calculated for E 11 c and E 11 u. The phonon parameters and the effective ionic charges of anions and cations for MOO, and PbMoO, crystals are determined. The diagrams of the splitting of the vibrational levels by thc Davydov resonance and by the factor group interactions have been determined. It is shown that the lattice radiation of crystals which have a number of vibrational oscillators (MOO,, PbMoO,) begins at low energy vibrational modes and at low values of the damping parameters.

The excitonic reflectivity spectra and the wavelength derivative reflection spectra have been investigated. The n = 1, n = 2 and n = 3 states of the A, B and C exciton series are determined. The exciton binding energies and exact values of the band gaps of all three intervals - , - and - have been calculated. Data on the splitting due to the crystal-field and the spin - orbit interaction are determined as well.

The optical anisotropy of the Sb2Se3 crystals was investigated at 300 and 11 K. Excitonic features of four excitons (A, B, C, and D) were observed in the optical spectra of the Sb2Se3 single crystals and in the photoelectric spectra of the Me–Sb2Se3 structures. The exciton parameters, such as the ground (n = 1) and excited (n = 2) state positions and the binding energy (Ry), were determined. The effective mass of the electrons at the bottom of the conduction band (m c * = 0.67m 0) as well as the holes at the four top valence bands (m v1 * = 3.32m 0, m v2 * = 3.83m 0, m v3 * = 3.23m 0 and m v4 * = 3.23m 0) were calculated in the Г-point of the Brillouin zone. The magnitude of the valence band splitting V1–V2 due to the spin–orbit interaction (Δso = 35 meV) and the crystal field (Δcf = 13 meV) were estimated in the Brillouin zone center. The energy splitting between the bands V3–V4 was 191 meV. The identified features were discussed based on both the theoretically calculated energy band structure and the excitonic band symmetry in the Brillouin zone (k = 0) for crystals with an orthorhombic symmetry (Рnma). The photoelectric properties of the Me–Sb2S3 structures were investigated in the spectral range 1–1.8 eV under E||c and E⟂c polarization conditions and at different applied voltages.

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