pH Effects on the Pulse Radiolysis of Deoxygenated Aqueous Solutions of Sulphur Dioxide

Abstract

Dilute deoxygenated aqueous solutions of sulphur dioxide and its related anions HSO–3 and SO2–3 in the pH-range 2–11 were pulse irradiated and the time dependence of the transient optical absorptions and electrical conductance recorded. Hydrogen atoms and OH radicals abstract hydrogen from HSO–3. Also OH radicals react with SO2 and SO2–3 to form the radical ion SO–3˙ with an absorption maximum at 255 nm. The SO–3˙ radical ions recombine to form sulphate (SO2–4) and dithionate (S2O2–6), the reaction rate and relative proportions of products being pH-dependent. In acid solutions the SO–2˙ radical ion with an absorption maximum at 360 nm is also formed, presumably by reaction of hydrogen atoms with sulphur dioxide. The SO–2˙ radical ions recombine to form dithionite (S2O2–4).