DFT Model of Elemental Sulfur in Sulfolane Solutions

The structure and the thermodynamic and optical (UV) properties of elemental sulfur solution in sulfolane (Sl) have been studied using density functional theory methods. The cyclic molecular form of sulfur (S₈ "crown") was found using PBE1PBE/6-311+G(d,p) approximation in combination with a polarizable continuum model (the integral equation formalism variant) to exist in sulfolane medium as a Sl-S₈-Sl solvate. It has been theoretically established that sulfur can form stable (S₈) clusters in concentrated solutions. An increase in the extent of association (n) of the sulfur cluster leads to a decrease in the extinction coefficient [TD-DFT(TPSSTPSS/6-311+G(d,p))] of the most intense absorption maximum lying at about 50,000 cm^-1 while maintaining the shape of the remaining part of the spectrum. The observed pattern qualitatively expresses the spectral regularities of solutions with different concentrations of sulfur in sulfolane. It has been proposed that a model of the absorption spectrum of elemental sulfur suggests a minor contribution of the S₁₂ molecular form (G₂₉₈^°((S₁₂)₂) - G₂₉₈^°((S₈)₃) ≈ -15.5 kJ mol^-1). The findings of the study will provide deeper insights into the transformation of molecular forms of sulfur and more precisely analyze processes involving sulfur as an acting species using electronic spectroscopy.