Rateconstants measured over the temperature range 2Cb2OO"C are reported for the following reactions: (a) reaction of the hydrated electron with oxygen, the proton, hydrogen peroxide, nitrate, nitrite, nitrobenzene and methyl viologen ; (b) reaction of the hydroxyl radical with another hydroxyl radical and ferrocyanide; (c) reaction of the hydrogen atom with permanganate and oxygen. To evaluate methods of estimating rate constants at high temperatures these rate constants and others in the literature have been fitted to the following equation: kobs = kdiff/(l + kdiff/kreact)where kobs is the measured rate constant for the bimolecular reaction in solution, kdiff is the encounter rate constant of the two reacting species, and k,,,,, is the rate constant that would be measured if diffusion of the species was not rate influencing. With the exception of reactions of the hydrated electron with nitrate and nitrite ions and nitrous oxide, good fits have been obtained to the above equation, and the results demonstrate that few, if any, of the reactions which are pertinent to water radiolysis are truly diffusion controlled at elevated temperatures.

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Reaction of the hyper-reduced metal ions Ni+, Cof and Cd+ with N 2 0 produces N2 and a hyperoxidised state M(III) of the metal ion by oxygen atom transfer. When formate is present a chain reaction occurs showing that CO; reduces M2+, and that M(II1) reacts with formate ion to produce CO,. Detailed studies of the chain reaction kinetics show that M(II1) exists in at least two forms, one probably being a hydrolysis product of the other. With nickel (and probably cadmium) M(III) is not stable and is either chemically similar to the hydroxyl radical or produces it on hydrolysis, e.g., H 2 0 MO+--tMO(OH) + H+ ' A. 0. Allen, C.