Isotope effect in Raman scattering spectra of 32S8–34S8 solid mixtures

Raman spectra of crystalline sulfur samples of the mixed isotopic composition (32S8)1−x(34S8)x, where 0 ≤ x ≤ 1, have been studied. These spectra demonstrate synchronization of oscillations of S8 molecules of the same isotopic composition which leads to "breathing" mode splitting at 211–216 cm−1 (Davydov splitting). The level of splitting depends on the molecule content of the corresponding isotope and attains its maximum value of 4.5 cm−1 for monoisotopic samples. If the molecules of different isotopic composition of 32S8 and 34S8 are adjacent, the difference in their eigen frequencies excludes the effect of splitting. For the other vibrational modes, the change in the relative content of 32S8 and 34S8 leads to proportional change in the intensity of the spectral bands with invariable frequencies of stretching vibrations or gradual change in the frequencies of lattice vibrations.