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