SPECTROSCOPIC STUDY OF LITHIUM HEXASULFIDE SOLUTIONS IN DMF

Solutions of lithium hexasulfide (Li2S6) in DMF have been investigated using UV-visible, Raman, IR and ESR spectroscopies. These techniques provide evidence of the equilibrium between S-6(2-) and S-3(-), which are the only polysulfides in these solutions. The absorption spectra o f these solutions have been decomposed. The contribution of the solven t and of the cell to the absorbance have been taken into account. It i s shown that the absorption bands of S-6(2-) can be considered as gaus sian. It is also shown that the calculation of the second derivative o f the visible absorption band of S-3(-) gives direct evidence of the v ibronic structure of this band. The decomposition of this vibronic str ucture into gaussian components gives an estimate of the frequency of the symmetric stretching mode of S-3(-) in the excited state. It is sh own that the S-6(2-) polysulfide, contrary to the S-3(-) polysulfide, displays significant differences when observed in DMF or liquid ammoni a: we discuss these differences.