Inhibition of Radiolytic Molecular Hydrogen Formation by Quenching of Excited State Water

Gregory P Horne,Simon M Pimblott,Jay A Laverne

doi:10.1021/acs.jpcb.7b02775

Abstract

Comparison of experimental measurements of the yield of molecular hydrogen produced in the gamma radiolysis of water and aqueous nitrate solutions with predictions of a Monte Carlo track chemistry model shows that the nitrate anion scavenging of the hydrated electron, its precursor, and hydrogen atom cannot account for the observed decrease in the yield at high nitrate anion concentrations. Inclusion of the quenching of excited states of water (formed by either direct excitation or reaction of the water radical cation with the precursor to the hydrated electron) by the nitrate anion into the reaction scheme provides excellent agreement between the stochastic calculations and experiment demonstrating the existence of this short-lived species and its importance in water radiolysis. Energy transfer from the excited states of water to the nitrate anion producing an excited state provides an additional pathway for the production of nitrogen containing products not accounted for in traditional radiation chemistry scenarios. Such reactions are of central importance in predicting the behavior of liquors common in the reprocessing of spent nuclear fuel and the storage of highly radioactive liquid waste prior to vitrification.

Highlights

The radiolysis of liquid water leads to a number of excited and ionized states of the medium that decay to the ground state or decompose to give water products.[1]
The nitrate anion (NO3−) has been used historically for probing the radiation chemistry that occurs in the radiolysis of water, eq 1, as its it is an effective scavenger precursor, and to of a the hydrated lesser extent tehleecHtronat(oemaq−,1)0−an12d
The data show a monotonic decrease in the yield of H2 with increasing NO3− concentration H2 is completely suppressed at very and high that the formation of NO3− concentration

Summary

■ INTRODUCTION

The radiolysis of liquid water leads to a number of excited and ionized states of the medium that decay to the ground state or decompose to give water products.[1]. Scavenging techniques in radiation chemistry involve observation of the stable product of interest while increasing the concentration of a solute that will react with its precursors. The nitrate anion (NO3−) has been used historically for probing the radiation chemistry that occurs in the radiolysis of water, eq 1, as its it is an effective scavenger precursor (epre−), and to of a the hydrated lesser extent tehleecHtronat(oemaq−,1)0−an12d. Recent picosecond pulse radiolysis experiments have provided NO3−, eq significant evidence for the 5, at sufficiently high NO3−. This reaction of H2O+ offers an additional pathway for NO3− decomposition to give a different product compared to normal radiolysis involving eqs 2 to 4. H2 yield with show that a nonelectron precursor plays an important role

■ METHODS

■ RESULTS AND DISCUSSION

■ ACKNOWLEDGMENTS

■ REFERENCES