FLASH PHOTOLYSIS STUDY OF SULFITE THIOCYANATE AND THIOSULFATE IONS IN SOLUTION

The primary photolytic processes, as observed by the technique of flash photolysis, were studied for the sulfur polyvalent anions SO32-, CNS-, and S2O32- in aqueous solution. Sulfite ions were found to produce two transient species, resulting from the primary photolytic process: SO32-·H2O →hv SO3- + eaq-. A short-lived species apparently formed by the addition of eaq- to sulfite ions and tentatively assigned to HSO32- (λmax 720 mμ) decays by first-order process, k = (1.9 ± 0.3) × 104 sec-1, and a longer lived species assigned to SO3- (λmax ∼275 mμ) decays by second-order process, 2k/ε = 1.5 × 106 at 275 mμ. Thiocyanate ions decompose on photolysis by at least two processes: CNS-·H2O →hv CNS + eaq- and CNS- →hv CN- + S. A transient spectrum, due to (CNS)2- radical anions, was found absorbing at λmax 485 mμ, with species decaying by a first-order process in air-free solutions and by a second-order process in the presence of oxygen. Thiosulfate ions decompose on photolysis by two processes: S2O32-·H2O →hv S2O3- + eaq- and S2O32-·H2O →hv S2O2- + OH + OH-. The OH radicals produced react with S2O32- to form S2O3- radicals. A transient optical spectrum with a λmax 380 mμ assigned to S2O3- decays by a second-order process in the absence of O2 and by a first-order process in the presence of O2. S2O2- has a λmax ∼280 mμ and decays by a second-order process in the presence or absence of oxygen. The CTTS absorption bands of the three sulfur anions have been determined. The esr spectra of the radicals produced on uv irradiation of SO32-, CNS-, and S2O32- ices at 77°K are given.