Sulfur-Containing Radical Anions Formed by Photolysis of Thiosulfate: Quantum-Chemical Analysis

The photochemistry of sodium thiosulfate (S2O3 (2-)) in aqueous solutions is rathercomplicated.Several sulfur-containing radical anions are formed upon photoexcitation.Any of them are rather common (SO3 & BULL;(-), SO2 (& BULL;-), and SO5 (& BULL;-)); others are rare (S2O3 (& BULL;-), (S4O6)-S-& BULL; (3-), and S & BULL;-) ornever documented (S2O5 (& BULL;-)). In order to support the identification of intermediate radicalanions, quantum-chemical (QM quantum mechanical) calculationsof the geometric and electronic structures of S2O3 (& BULL;-), S2O5 (& BULL;-), and (S4O6)-S-& BULL; (3-) were performed. Two different approaches, time-dependent densityfunctional theory and complete active space self-consistent field,were applied to identify the method optimal for the reproduction ofthe experimental electronic absorption spectra. Several of the mostcommonly used functionals were considered. The best agreement withthe experimentally observed spectra of reference compounds (commonsulfur-containing anions and radical anions) was achieved for theWB97X-D3 functional. Using this approach, satisfactory agreement betweenexperimental and calculated spectra of S2O3 (& BULL;-), S2O5 (& BULL;-), and (S4O6)-S-& BULL; (3-) was achieved. It was shown that S2O5 (& BULL;-) and (S4O6)-S-& BULL; (3-) can exist in two isomeric forms with different spectral properties.These isomers are S2O3O2 (& BULL;-); SO3SO2 (& BULL;-) for thecase of S2O5 (& BULL;-) and(S2O3)(2) (& BULL;3-); (S3O3 (2-)...SO3 (& BULL;-)) for the case of (S4O6)-S-& BULL; (3-).