Effect of electron energy on the radiation chemistry of liquid water

The dependence of the radiation chemistry of water on electron energy is probed using Monte Carlo track-structure simulation and stochastic modeling of diffusion kinetics. Decreasing the initial electron energy from 1 MeV to 100 keV has little effect on the decay kinetics of e(aq)^- and OH or the formation of Ha and H₂O₂. In the energy range 100 keV to 1 keV, the initial electron energy has a considerable effect on the chemistry; decreasing the electron energy increases the amount of intratrack reaction, lowering the long-time yields of e(aq)- and of OH and raising the yields of the molecular products. For electrons of initial energy lower than 1 keV, these trends in the kinetics are reversed; the amount of reaction decreases and there is more e(aq)- and OH surviving intratrack reactions with less H₂ formed. The changes in the radical chemistry and product formation are due to changes in the relative distributions of the reactants produced by the primary ionization and excitation events. The reversal at low energies occurs because the local density of reactive species in low-energy tracks is similar to that in the (larger) spurs of high-energy tracks.