Source of Molecular Hydrogen in High-Temperature Water Radiolysis

Abstract

Molecular hydrogen is a primary product of the interaction of low-LET (γ, β) radiation with water, and previous measurements have shown that its initial yield increases at elevated temperature. This has been the subject of controversy because more atomic H and (e(-))aq free radicals escape recombination at elevated temperature, and the corresponding production of H2 should decrease. Room temperature experiments have demonstrated that a large fraction of H2 also comes from early physicochemical processes (presumably electron-hole charge recombination and/or dissociative electron attachment), which can be suppressed by scavenging presolvated electrons. In the present work we extend these scavenging measurements up to 350 °C to investigate why the H2 yield increases. We find that most of the H2 yield increase is due to the "presolvation" processes. Relatively small changes in the scavenging efficiency vs LET, and a significant effect of temperature depending on the (positive or negative) charge of the scavenger, indicate that the presolvation H2 is dominated by electron-hole charge recombination rather than dissociative electron attachment at all temperatures.

Hydrogen from Radiolysis of Aqueous Fluid Inclusions during Diagenesis

“…Hydrogen formation by radiolysis may increase with elevated temperature [37]. However, the sylvite and halite sampled in this study have not been subject to very high temperatures.…”

Reaction rate of H atoms with N2O in hot water

“…The experimental method is described in detail in previous publications 16,20 . Briefly, two HPLC pumps were used to generate a total high pressure flow of 6 mL/min.…”

Generation of Ultrafast Transient Acid Spikes in High-Temperature Water Irradiated With Low Linear Energy Transfer Radiation

“…Although H 2 is a molecular product, g(H 2 ) is observed to continue to increase with temperature, particularly above 200°C. This anomalous increase in g(H 2 ), which is an issue of much debate in the radiation chemistry of high-temperature water, has been discussed at length elsewhere [48][49][50][51][52][53][54][55]. From a theoretical perspective, we have recently performed Monte Carlo track chemistry simulations of the low-LET radiolysis of liquid water over the range 25-350°C [51], incorporating newly measured or re-assessed experimental data.…”