The samples of GeS_1.35 glasses were synthesized with germanium and sulfur of natural isotopic composition and with isotopically enriched germanium (⁷²Ge, ⁷⁴Ge, ⁷⁶Ge). The glasses were investigated by the method of Raman scattering spectroscopy (RSS). It was shown that GeS_4/2 tetrahedrons and structural units containing Ge[sbnd]Ge homobonds are present in glasses. The quantum-mechanical calculation of the frequency of fundamental vibrational modes in glass network was carried out. Their dependencies on the atomic mass of germanium were used for identification of bands in RS (Raman scattering) spectra.