On the temperature dependence of the primary yield and the product Gεmax of hydrated electrons in the low-LET radiolysis of liquid water

Abstract

Monte-Carlo simulations are performed to calculate the temperature dependence of the primary hydrated electron yield (Geaq-) for liquid water irradiated by low linear-energy-transfer radiation (LET ~ 0.3 keV µm–1) in the range 25–325°C. Calculations are carried out by taking properly into account the effect of the time and temperature dependencies of the water dielectric constant on the electron–cation geminate recombination. Our computed Geaq- values slightly increase with increasing temperature, in good agreement with experiment. The product Geaq- εmax(eaq-), estimated by using existing experimental data of the maximum molar extinction coefficient εmax(eaq-), remains nearly constant or slightly increases, depending on the temperature dependence chosen for εmax. Our Geaq-εmax(eaq-) values compare generally well with most experimental data, as well as with the predictions of deterministic diffusion-kinetic model calculations. Moreover, our results indicate that the static dielectric constant of water (εs) does not play any significant role on the electron–cation recombination at early times. Such a finding is inconsistent with the interpretation, proposed by certain authors in the literature, that Geaq- should in fact decrease as temperature is increased because of an increased electron–cation geminate recombination due to a lowering of εs. Finally, the temperature dependence of the hydrated electron yields, calculated at various times between 10 ps and 1 µs, shows that at low LET, the time required to establish homogeneous chemistry in the bulk of the solution is ~10–6 s in the range ~25–100°C, and that this time diminishes to ~10–7 s at higher temperatures. Key words: liquid water, radiolysis, temperature, hydrated electron (eaq-), radiolytic yields, electron–cation geminate recombination, dielectric constant, molar extinction coefficient of eaq-, homogenization time.