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The flash photolysis of ceric sulfate and ceric nitrate in aqueous solutions was studied. Ceric sulfate produced a transient species with an optical absorption maximum at 4550 A which decays bimolecularly with k = 6.5 ± 1.3 X 10s M~l sec-1 and is assigned to the HSCh free radical. Ceric nitrate gave rise to an optical spectrum with maxima at 5950, 6400, and 6750 A. This intermediate was identified as the NO3 radical by its characteristic absorption spectrum in the visible region. It was found to decay by a first-order process with k = 9.5 X 102 3sec-1. In addition, a new ultraviolet band with maxima at 3350 A is reported. The main primary photolytic process in both sulfate and nitrate salts is explained on the basis of a charge transfer from the hydration sphere to the Ce(IV) ion: Ce(IV) -H20 -t Ce(III) + OH + H+, followed by reactions OH + HS04-HS04 + OHand OH + HNO3 -> NO3 + H20. Evidence for this mechanism was derived from the extrapolation to "zero" time of the pseudo-first-order decay plots in presence of various additives. The decrease of the "initial" concentration of HS04 and X03 produced was found to be proportional to the /c(OH + S) X Cs values of the solutes used. The rate constants for the reaction of HS04 and XO3 with added solutes-formate, acetate, methanol, ethanol, 2-propanol, thallous ions, and cerous ions-were obtained. HS04 is found to be a stronger oxidizing agent than X03 although HS04 is not as strong as OH radicals.

Abstract— Kinetic data are reported for the thermal decay of colored transients formed by U.V. irradiation of aqueous solutions of 2‐nitrotoluene. The transients display an acid‐base equilibrium with a pK value of 3.7. The decay is catalyzed by acids and the following rate constants in liter sec‐l mole‐1 were evaluated for the base form of the transient reacting with an acid at 30.0°C: 3.5 × 10‐3 (H2O), 2.6×103 (CH3COOH), 4.7×104 (+NH3CH2COOH) and 4.2×105(H+).