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 H2O molecules is a possible pathway for the formation of part of the initial H-2 yield. Comparison of recent dissociative-electron-attachment H--anion yield-distribution measurements from amorphous H2O 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.