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Issue 4, 1988
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Ionisation constants of ˙OH and HO˙2 in aqueous solution up to 200 °C. A pulse radiolysis study

Abstract

The ionisation constant of ˙OH has been determined up to 200 °C from measurements of its rate of reaction with CO2–3 in alkaline solution, where O˙– is unreactive. The Van't Hoff plot shows the same curvature as that for Kw, so that ˙OH and H2O have the same heats of ionisation. ΔH for the equilibrium ˙OH + OH⇌ O˙–+ H2O is independent of temperature and equal to –15.4 ± 0.5 kJ mol–1. ΔH for the ionisation of HO˙2 has been measured as zero within experimental error up to 175 °C by determining the concentrations of HO˙2 and O˙–2 at equilibrium from optical absorbance measurements. The activation energies for the reaction of ˙OH with CO2–3 and HCO3 are independent of temperature and equal to 23.6 ± 0.4 and 21.2 ± 0.2 kJ mol–1, respectively, although k(˙OH + CO2–3)≈ 50 k(˙OH + HCO3). The G values for eaq and ˙OH increase by 27% between 20 and 200 °C in the pH range 4.4–9.2, but appear to be independent of temperature at pH 2.

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Article type: Paper
DOI: 10.1039/F19888401113
Citation: J. Chem. Soc., Faraday Trans. 1, 1988,84, 1113-1121
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    Ionisation constants of ˙OH and HO˙2 in aqueous solution up to 200 °C. A pulse radiolysis study

    G. V. Buxton, N. D. Wood and S. Dyster, J. Chem. Soc., Faraday Trans. 1, 1988, 84, 1113
    DOI: 10.1039/F19888401113

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