On the dissociative electron attachment as a potential source of molecular hydrogen in irradiated liquid water

In the radiolysis of liquid water, different mechanisms for the formation of molecular hydrogen (H 2) are involved at different times after the initial energy disposition. It has been suggested that the contributions of the e aq − + e aq −, H + e aq − and H + H reactions between hydrated electrons (e aq −) and hydrogen atoms in the spurs are not sufficient to account for all of the observed H 2 yield (0.45 molecules/100 eV) on the microsecond time scale. Addressing the question of the origin of an unscavengeable H 2 yield of 0.15 molecules/100 eV produced before spur expansion, we suggest that the dissociative capture of the so-called vibrationally-relaxing electrons by H 2O molecules is a possible pathway for the formation of part of the initial H 2 yield. Comparison of recent dissociative-electron-attachement H −-anion yield-distribution measurements from amorphous H 2O films with the energy spectrum of vibrationally-relaxing electrons in irradiated liquid water, calculated by our Monte Carlo simulations, plays in favor of this hypothesis.