Density dependence of the yield of hydrated electrons in the low-LET radiolysis of supercritical water at 400 °C: influence of the geminate recombination of subexcitation-energy electrons prior to thermalization

Abstract

Monte Carlo simulations were used to calculate the yield of hydrated electrons (e_aq⁻) in the low-linear energy transfer radiolysis of supercritical water at 400 °C as a function of water density over the range of ∼0.15 to 0.6 g cm⁻³. Very good agreement was found between our calculations and picosecond pulse radiolysis experimental data at ∼60 ps and 1 ns at high density (>0.35 g cm⁻³). At densities lower than ∼0.35 g cm⁻³, our e_aq⁻ yields were lower than the experimental data, especially at ∼60 ps. However, if we incorporated into the simulations a prompt geminate electron–cation (H₂O˙⁺) recombination (prior thermalization of the electron) that decreased as the density decreased, our computed e_aq⁻ yields at ∼60 ps and 1 ns compared fairly well with the experimental data for the entire density range studied.