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Hydrogen atom formation in the gamma and heavy ion radiolysis of aqueous systems
[Thesis]. Manchester, UK: The University of Manchester; 2010.
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Abstract
Experimental measurements in conjunction with stochastic simulations are used to determine hydrogen atom yields in the gamma and heavy ions radiolysis of aqueous solutions of formate and deuterated formate ions.In radiolysis, the hydrogen atom is produced directly by the fragmentation of water excited states, and during the diffusion-kinetic evolution of the radiation track by the intra-track reaction of eaq- with Haq+ up to the microsecond timescale. The yield of H• is relatively small, but it is fundamentally very important. An accurate examination of the H atom yields after radiolysis will make possible a better understanding of the initial steps of the radiolytic decomposition of water. The competition between H atom combination reactions and its formation by reaction of eaq- with Haq+ makes predictions of the H atom kinetics very difficult. Hydrogen atom yields were determined by difference measurements of H2 yields and directmeasurements of HD yields when using deuterated formate as H• scavenger. While the total H2 yield measured is always greater for alpha than for gamma radiolysis, the H atom yield is observed to be smaller. The addition of selected scavengers of the hydrated electron and its precursors reveals a stronger correlation of the H atom formation on the precursor to the hydrated electron rather than the hydrated electron itself. Scavengable H• yields strongly decrease as the concentration of the electron scavenger increases.Stochastic track chemistry calculations were used to analyze the measured experimental yields and to elucidate the underlying kinetics.