M. Fischer et P. Warneck, PHOTODECOMPOSITION AND PHOTOOXIDATION OF HYDROGEN SULFITE IN AQUEOUS-SOLUTION, Journal of physical chemistry, 100(37), 1996, pp. 15111-15117
A zinc are lamp and a mercury lamp, respectively, were used to study t
he photodecomposition of HSO3- and SO32- in aqueous solutions saturate
d with either argon or nitrous oxide. The main products in both cases
were sulfate and dithionate, which are attributed to arise from the se
lf-reaction of SO3- radicals. Quantum yields for the formation of SO3-
in argon-saturated solution based on hydrazoic acid and/or ferric oxa
late actinometry were 0.19 +/- 0.03 for HSO3- and 0.39 +/- 0.03 for SO
32-, essentially independent of S(IV) concentration. In both systems,
the rate of sulfate formation rose with time at the expense of that of
dithionate, This is explained by reactions of hydrogen atoms and hydr
ated electrons with dithionate (rate coefficient k(5) approximate to 2
x 10(5) dm(3) mol(-1) s(-1)). N2O as a scavenger for these radicals r
emoved the effect and raised the quantum yields to 0.25 +/- 0.03 and 0
.75 +/- 0.04, respectively. The product ratios under these conditions
were [S2O62-]/[SO42-] = 0.43 +/- 0.04 for HSO3- and 0.61 +/- 0.03 for
SO32-. In oxygen-saturated solutions, the photolysis of HSO3- led to a
short chain reaction with sulfate and peroxodisulfate as products. Th
e latter product was assigned to arise from the recombination of SO5-
radicals. Steady state analysis of the product evolution with time gav
e rate coefficients for two of the reactions involved: k(16)(SO5- + HS
O3-) = (1.2 +/- 0.4) x 10(4) dm(3) mol(-1) s(-1) for the main propagat
ion reaction and k(19a)(HO2 + SO5-) = (1.8 +/- 1.0) x 10(9) dm(3) mol(
-1) s(-1) for the principal termination reaction. These values agree w
ell with recent data from radiolysis experiments.