Kinetic evidence for excited water in the Cobalt-60 γ-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(¹Δ_g). 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: G_H= 3.67 ± 0.03, k_H,Fe2 +/k_H,O2=(12.0 ± 0.5)× 10^–4, G(Fe³⁺)_deaer.(at [Fe²⁺]= 0)= 7.68 ± 0.04, G_H2O^*= 0.49 ± 0.05, k_H2O^*/k_{H2O^*,Fe²⁺}=(15.0 ± 4.0)× 10^–3, k_H2O^*,O2/k_{H2O^*,Fe²⁺}= 11.7 ± 3.2., The lifetime of the excited water is estimated to be not less than 10^–7 s.