Knowledge Bank

The energy levels, charge distributions, and other properties of sulfur chains, $So,n=2,3,\dots 8$; sulfur rings, $Sa,n=4,6,7,8,12$; and sulfanes, $H2So,n=2,3,\dots 8$, were computed by the use of extended Hueckel theory. Different isomers and conformers, including branched species, were considered. Predicted spectral transitions for the sulfane chains and sulfur rings coincide with the observed transitions which lie in the UV. Sulfur chain molecules have low-lying excited states. Therefore, transitions from more deeply buried filled orbitals to the excited levels occur in the visible region and cause diradical chains to be deeply colored. Calculations fit the observed spectra of $S2$, $S2$, and $S1$, and predict that larger chains should be black. Since polymeric sulfur chains are light yellow, we conclude that polymeric sulfur is not a diradical chain, but that the chains are terminated by hydrogen or ring closure or by complexing with other species.