PULSE-RADIOLYSIS STUDY OF CONCENTRATED SULFURIC-ACID-SOLUTIONS - FORMATION MECHANISM, YIELD AND REACTIVITY OF SULFATE RADICALS

In the pulse radiolysis of concentrated sulfuric acid solutions, the absorption spectrum and the molar absorption coefficient (1600 dm3 mol-1 cm-1) of the sulfate radical are unchanged up to 10 mol dm-3 H2SO4, suggesting that the sulfate radical exists in the dissociated form (SO4-). Two formation processes for the sulfate radical have been directly demonstrated in sulfuric acid and hydrogensulfate solutions: a fast one completed in the duration of the electron pulse, and a slow one occurring over a microsecond time range. For sulfate solutions only the fast formation process is observed. In sulfuric acid solutions the slow formation process is OH + HSO4- --> H2O + SO4- (4.7 x 10(5) dm3 mol-1 s-1) and OH + H2SO4 --> HSO4 + H2O --> SO4- + H3O+ (1.4 x 10(7) dm3 mol-1 s-1), and the fast formation process is the direct action of radiation on sulfuric acid with a G value of (2.7 + 0.4) X 10(-2) molecule eV-1. The yields of (OH + SO4-) and H can be quantified as: G(OH + SO4-) = 2.9f(w) + 2.7f(s) and G(H) = 3.7f(w) + 2.7f(s). The yields of SO4- have also been evaluated and the decay kinetics and reactions of the sulfate radical studied.