Yields of H2 and hydrated electrons in low-LET radiolysis of water determined by Monte Carlo track chemistry simulations using phenol/N2O aqueous solutions up to 350 °C

Abstract

The effect of temperature on the yields of H₂ and hydrated electrons (e_aq⁻) in the low linear energy transfer (LET) radiolysis of liquid water has been modeled by Monte Carlo track chemistry simulations using phenol/N₂O aqueous solutions from 25 up to 350 °C. N₂O was used to scavenge e_aq⁻ and H˙ atoms formed in spurs giving N₂ as a product. The primary aim of this work is to elucidate the main factors that account for the anomalous increase in the H₂ yield with temperature. Comparing our calculated H₂ and N₂ yields with experiments led us to re-evaluate certain parameters involved in radiolysis, such as the H⁻/H₂O dissociative electron attachment (DEA) cross section and its variation with temperature. Most importantly, we found that the prompt DEA process largely dominates the temperature dependence of the primary yield of H₂ over most of the temperature range considered. Unlike what has been proposed by some authors in the literature, our simulations showed that the oxidation of water by H˙ atoms contributes only ∼12% of the total g(H₂) at 350 °C and is thus insufficient to quantitatively explain, by itself, the increase in g(H₂) with temperature that is observed experimentally above 200 °C.