Laser photolysis study on reactions of sulfate radical and nitrate radical with chlorate ion in aqueous solutions Formation and reduction potential of ClO3 radical

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Abstract
Electron transfer reactions of sulfate radical anion (SO 4 - ) and nitrate radical (NO 3 ) with chlorate ion (ClO 3 - ) have been studied by laser photolysis. Reaction (1) leads to the formation of chlorine trioxide radical (ClO 3 ) which has an absorption peak at 330 nm. Simulation work gave estimated results including: the forward and reverse rate constants of reaction (1), [k f =(4.0±0.5)×10 6 dm 3 mol -1 s -1 , k r =(5±5)×10 5 dm 3 mol -1 s -1 at ionic strength I=0], the second-order decay rate constant of ClO 3 [2k=(9.0±1.6)×10 8 dm 3 mol -1 s -1 ], and its molar absorption coefficient [ε=(1500±250) dm 3 mol -1 cm -1 at 330 nm]. Reaction (2) was also observed and the forward and reverse rate constants were determined to be k f =(9.0±1.2)×10 3 dm 3 mol -1 s -1 and k r =(8.3±1.0)×10 2 dm 3 mol -1 s -1 . The equilibrium constant K of reaction (2) was determined to be 42±6, from the observed absorbance of the radicals at equilibrium. The reduction potential of ClO 3 , E 0 (ClO 3 /ClO 3 - ) was deduced to be 2.35±0.05 V vs. NHE when E 0 (NO 3 /NO 3 - ) is taken as 2.45±0.05 V vs. NHE.

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