Dependence of Molecular Hydrogen Formation in Water on Scavengers of the Precursor to the Hydrated Electron

Abstract

Molecular hydrogen yields have been measured in the γ radiolysis of aqueous solutions with a wide variety of scavengers of the hydrated electron and its precursors. A decrease in molecular hydrogen yield with increasing scavenging capacity of the hydrated electron is found with all solutes. Scavengers with particularly high rate coefficients for reaction with the precursors to the hydrated electron compared to the hydrated electron, such as selenate and to a lesser extent molybdate, show a more rapid decrease in hydrogen yields with increasing scavenging capacity than is observed with the other solutes. The yield of molecular hydrogen is better parametrized by the scavenging capacity for the precursors to the hydrated electron than by the scavenging capacity for the hydrated electron. Good scavengers of precursors to the hydrated electrons do not exhibit a "nonscavengable" hydrogen yield in the high scavenging capacity limit. These results suggest that the previously accepted "nonscavengable" yield of molecular hydrogen is due to precursors of the hydrated electron and it can be lowered with appropriate scavengers.

Probing the Influence of X-rays on Aqueous Copper Solutions Using Time-Resolved in Situ Combined Video/X-ray Absorption Near-Edge/Ultraviolet−Visible Spectroscopy

“…22,23,[25][26][27] At low solute concentrations the interactions between the radiolysis products of water and the solute will prevail, but at higher solute concentrations also the products of the radiolysis of the solute and the interaction with their environment may start to play an important role. Therefore, if one wants to study the effect of the radiolysis products of water on a certain system, solute concentrations should be kept as low as possible.…”

“…Reduction of Cu 2+ in the presence of chloride and bromide anions, but not in the case of nitrate and sulfate, can be explained by the ability of the nitrate and sulfate to scavenge the hydrated electron, whereas the chloride and bromide are known to be possible OH • radical scavengers. 13,25,35 Indeed with the exception of the imidazole ligand, in every case when the [SO 4 2-] is high (100 mM), copper reduction is suppressed. This leads us to conclude that the hydrated electron is most likely to be responsible for reduction of the copper in this solution, but it is not clear whether this occurs via direct interaction with the Cu 2+ or via the ligand.…”

Water Radiolysis: Influence of Oxide Surfaces on H2 Production under Ionizing Radiation

“…The first three reactions in Table 2 are responsible for most of the formation of H 2 , i.e., around 70% of the observed yield in the  radiolysis of water [52,53]. In this latter case, as the hydrogen atom yield is much smaller than that of the hydrated electron (see Table 1), most of the H 2 produced is due to the reaction between two hydrated electrons.…”

“…In this latter case, as the hydrogen atom yield is much smaller than that of the hydrated electron (see Table 1), most of the H 2 produced is due to the reaction between two hydrated electrons. Moreover, recent studies have proven that the remainder of the H 2 formation is due to the precursor of the hydrated electron [53]. It has been suggested that the mechanism responsible is the dissociative recombination of the water cation and a non-hydrated electron [53,54].…”

On the Temperature Dependence of the Rate Constant of the Bimolecular Reaction of Two Hydrated Electrons

“…Recent studies have shown that a major fraction of the total H 2 formed [g(H 2 ) = 0.45 molecule/100 eV at 25°C (for conversion into SI units, 1 molecule per 100 eV ≈ 0.10364 μmol J -1 )] is due to reactions involving the precursors of the hydrated electron at short (< 1 ps) times after the initial passage of the radiation [17,18]. These reactions include the dissociation of excited water molecules formed by recombination of the nonhydrated electron with its parent cation H 2 O + (geminate recombination) and the dissociative attachment of subexcitation-energy electrons (those that have kinetic energies lower than the firstelectronic excitation threshold of the medium, i.e., ~7.3 eV in liquid water) to a water molecule (DEA) [19].…”