Vibrational spectroscopic investigations of snse8-n molecules

The fundamental vibrations of 13 cyclic S_nSe_8-n (n = 7—2) molecules have been calculated using a modified Urey—Bradley force field with 9–14 independent force constants whose values have been adapted from those of Se₈ and S₈. Calculated wavenumbers are compared to those obtained by Raman spectroscopy for sulfur—selenium phases prepared by recrystallizing quenched molten mixtures of the elements as previously described. Agreement between the observed spectra and calculated wavenumbers is closest by assuming the existence of selenium—selenium bonds and the absence of isolated selenium atoms in S_nSe_8-n molecules. It is assumed that sulfur—selenium phases are mixed crystals with the following components in varying concentrations: 1,2-S₆Se₂, 1,2,3-S₅Se₃, 1,2,3,4-S₄Se₄, 1,2,5,6-S₄Se₄, 1,2,3-S₃Se₅ and 1,2-S₂Se₆. The presence of S₈ and Se₈ in some of the phases is indicated by the Raman spectra.