Salt effect on ionic reactions in supercritical water

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Temperature ahd pressure effects on reactions of hydrated elelctrons and OH radical have been studied near the critical temperature of water. The reaction rates were measured using pulse radiolysis technique. The time resolution is about 5 nano-seconds. Reaction between hydrated electron and nitrobenzene is close to a diffusion limit. The reaction rate, however, sharply slow down near the critical temperature. Reaction rates between hydrated electron and N_2O can be explained by the Marcus electron transfer model.Reaction rates of OH radical with H_2 in high temperature water are 10 times faster than those in gas phase. Near 350 C, however, the reaction rates in water slow down and approach to the reaction rate in gas phase. These differences in the reaction rates can be explained by considering hydration of reactants including transition state. A similar reaction model predicts that reaction of OH with benzene in water could be faster than that in gas phase even near 350 C. Therefore the reaction rates of OH with benzene in gas phase cannnot be applicable in high temperature water.