Kinetic Evidence for Excited Water in the Cobalt-60 y-Radiolysis of Ferrous Sulphate in 0.4 mol dm-3 Sulphuric Acid Solutions

Abstract

The effect of oxygen and ferrous ion concentrations on G(Fe3+) from ferrous sulphate in 0.4 mol dm–3 sulphuric acid solution irradiated with 60Co γ-rays has been studied. The results cannot be fully explained in terms of the accepted reaction mechanism. The marked increase in G(Fe3+)deaer. with ferrous ion concentration is attributed to a reaction between ferrous ion and excited water in competition with pseudo first-order decay of the excited water. In the presence of oxygen the results are consistent with a competing reaction between excited water and oxygen to give hydrogen sesqui-oxide, H2O3, or singlet oxygen, O2(1Δg). Homogeneous kinetics describe the data with good precision for ferrous ion concentrations ranging from 0.2 to 100 mmol dm–3 and for oxygen concentrations ranging from 0.0 to 1.1 mmol dm–3. The method of least-squares was used to obtain the following parameters from the data: GH= 3.67 ± 0.03, kH,Fe2 +/kH,O2=(12.0 ± 0.5)× 10–4, G(Fe3+)deaer.(at [Fe2+]= 0)= 7.68 ± 0.04, GH2O*= 0.49 ± 0.05, kH2O*/kH2O*,Fe2+=(15.0 ± 4.0)× 10–3, kH2O*,O2/kH2O*,Fe2+= 11.7 ± 3.2., The lifetime of the excited water is estimated to be not less than 10–7 s.