Radiation chemistry of solid thiosulfate: optical absorption spectra

Solid sodium thiosulfate, anhydrous and hydrated (5 H2O), was irradiated wi th 10 MeV electrons in a pulsed, high-dose (30 kGy) rate regime. The result ing optical absorption was measured by diffuse reflection spectophotometry (DRS) (absorption band in anhydrous salt at 360 mm, in hydrated salt at 418 nm). Absorption decays occurred at t(1/2) = 80 h (anhydrous) and t(1/2) = 9 h (hydrated) at room temperature. The yellowish radical ion formed in irr adiated anhydrous thiosulfate was identified as [(S2O3)-S-.](-), and not [( S2O3)-S-.](3-), as proposed in previous nonoptical (EPR) investigations. Th e absorption spectrum of [(S2O3)-S-.](-) in a solid matrix was similar to t he transient spectrum ascribed to the same radical, obtained by pulse radio lysis in aqueous solution, and had a lifetime many orders of magnitude shor ter. A similar radical anion, but in the complex with adjacent water molecu les from the hydration moiety, was observed in hydrated thiosulfate (Na2S2O 3. 5 H2O).