A. John Elliot

Temperature dependence of g values for H2O and D2O irradiated with low linear energy transfer radiation

The g values for the primary species formed in the γ-radiolysis of light and heavy water have been measured as a function of temperature up to 300 °C. With the exception of g(H2) and g(D2), all the g values are consistent with the generally accepted diffusion-kinetic model of spurs, i.e. with an increase in temperature, the g values of the free radicals increased while those of peroxide decreased. The g values for H2 and D2 increased with temperature which suggests that they are formed by other mechanisms in addition to radical–radical reactions in the spur.

Temperature dependence of the rate constant for the reaction e–aq+ OH in water up to 150 °C

The temperature dependence of the rate constant for the reaction, e–aq+ OH → OH–(1) has been measured in liquid water up to 150 °C. The values of k1 were derived from fitting the absorbance vs. time plots of the decay of the hydrated electron in pulsed-irradiated deoxygenated 1× 10–3 mol dm–3 sodium borate solutions using the computer programme FACSIMILE. The values for k1 were (2.8 ± 0.2)× 1010(18 °C), (5.0 ± 0.4)× 1010(75 °C), (6.0 ± 0.5)× 1010(100 °C) and (7.2 ± 0.3)× 1010 dm3 mol–1 s–1(150 °C). The temperature dependence of k1 was found to be much less than for diffusion in water. The temperature dependence of Iµmax for the hydrated electron has been determined up to 200 °C.

Temperature dependence of the rate constant for the reaction H + OH in liquid water up to 200 °C

The temperature dependence of the rate constant, k1, for the reaction H + OH → H2O (1) has been determined in water up to 200 °C by pulse radiolysis of 10–2 mol dm–3 HClO4 solutions. Values of k1 were derived using the computer code FACSIMILE to simulate the measured absorbance vs. time profile of OH at 250 nm. Required values of k2 and k3 for the simultaneously occurring reactions H + H → H2(2) and OH + OH → H2O2(3) were taken from the literature. Although k2 has the temperature dependence of a diffusion-controlled reaction, a statistical spin factor of 0.25 must be included for k2 to be described by the Smoluchowski equation. Conversely, a statistical spin factor of 1 is required to account for the values of k1 and k3. The temperature dependences of k1 and k3 are similar to one another but significantly less than that for k2, consistent with the chemical reaction step becoming dominant at elevated temperatures in the reactions (1) and (3). These results are interpreted qualitatively in terms of transition-state theory.

Pulse radiolysis of lodate in aqueous solution

The reactions of primary water radiolysis radicals with IO–3 have been re-investigated using electron pulse radiolysis and absorption spectroscopy. Rate constants for iodate reaction with e–(aq)[(5.45 ± 0.45)× 109 dm3 mol–1 s–1], O˙–[(1.82 ± 0.04)× 109 dm3 mol–1 s–1] and ˙OH (< 105 dm3 mol–1 s–1) have been measured and compared with previously determined values. The observed iodate concentration dependence of the two transient absorptions produced by its reaction with the hydrated electron and the oxide radical were found to be due only to spur scavenging effects, and thus the dimerization equilibria proposed by previous workers is not necessary. The previously reported rate constants for the reaction of iodate with hydroxyl radicals have been shown to be due to just iodate reaction with the small concentration of O˙– present in equilibrium with the hydroxyl radical.