Photochemistry of sodium tetrathionate in aqueous solutions

Photochemistry of tetrathionate anion S₄O₆²⁻ in aqueous solutions was studied by means of stationary photolysis and laser flash photolysis. Quantum yield of S₄O₆²⁻ disappearance was found to change from 0.05 to 0.2 depending on the irradiation wavelength and the presence of dissolved oxygen. Deep photolysis leads to the sol formation. S₂O₃^•- radical absorption was detected in the laser flash photolysis experiments. For quantitative description of the laser flash photolysis data, two channels of S₄O₆²⁻ photodissociation were proposed. The first channel yields in formation of two S₂O₃^•- radical anions; in the second channel S₂O₃^•- and SO₃^•- radical anions and a sulfur atom are formed. Surprisingly, the results of the laser flash photolysis experiments did not depend on the presence of dissolved oxygen. This fact was explained by the formation of the weakly-bound van der Waals complexes [S₄O₆²⁻…O₂]. At the experimental conditions all the dissolved oxygen molecules are bound and cannot react with the primary radical anions. In conditions of stationary photolysis, oxygen is photochemically released and can react with other intermediates, increasing the quantum yield of tetrathionate photodecomposition.