The experiments of Baxendale, Evans and Park5 on the initiation of vinyl polymerization by ferrous ions and hydrogen peroxide provide good evidence for the participation of OH radicals, but steps (2) and (a) have not had similar experimental confirmation.The present experimental investigation of the iron + H,O, system which we now report has revealed several new features incompatible with the details of the Haber and Weiss chain mechanism. A short account of our work has been given elsewhere.6 We conclude that the reaction producing oxygen is not that of HO, with hydrogen peroxide but HO, or 0,' with the ferric ion, and we propose a new chain mechanism with OH, HO, and ferrous ion as carriers. The same chain mechanism interprets sa.tisfactorily many aspects of the ferric ion catalyzed decomposition of hydrogen peroxide, as will be shown in Pa.rt I1 of this work.

The quantum yield for the photolysis of hydrogen peroxide by 2537 8, light in 0.10 N perchloric acid is found to be 1-00 at 25" C and is independent of concentration and light intensity over the ranges studied, viz., 2 x 10-5 to 0.1 M peroxide and 4.5 x 10-6 to 5 X 10-4 einstein 1.-1 min-1. The yield falls to 0.80 at 4" C. The ion HO2-gives the same yields as H202 at these temperatures. The presence of Cu2+ introduces a chain reaction in otherwise non-chain conditions. From this it is inferred that in the non-chain decomposition HO2 is an intermediate and the observed quantum yield is twice the primary yield.In the absence of air, formic acid, carbon monoxide, ethanol and isopropanol also induce the chain decomposition of hydrogen peroxide. On the other hand acetic acid decreases the quantum yield until it reaches 0.50 when it is independent of acetic acid concentration. This is considered additional evidence that the primary yield is 050 at 25" C. In the presence of air all the organic compounds reduce the quantum yield to less than 0.50, which means that peroxide is regenerated in these conditions.

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The transient absorption produced by the pulse radiolysis of CNS-is shown to be due to (CNS)z formed by the reactions : 1 OH+CNS-+OH-f CNS, CNS + CNS-+ (CNS) .;The rate constants of reactions (l), (2) and (3) at 22°C determined from kinetic and equilibrium measurements are 2-8 x lolo, 7.0 x lo9 M-l sec-l and 3.4 x lo4 sec-l, respectively. For iodide ion, which forms I2 in the same way, the equilibrium constant for Iz formation is 1.13 x lo5 M-l.The corresponding kinetic constants cannot be determined as accurately as for CNS-but are estimated to be 3-4 x lolo, 7.6 x lo9 M-' sec-l and 6 x lo4 sec-'. 2 3Previous pulse radiolysis and flash photolysis studies 1-4 on the halide ions have shown that, following the production of the halogen atom by oxidation or photolysis, the diatomic ion is formed, e.g., HzO-+H, OH, e; Y I-+ OH+I + OH-I + 1-4,. EXPERIMENTALThiocyanate and iodide were used as the potassium salts. Solutions of pH 2 and 7 were made with perchloric acid and a phosphate buffer respectively. These materials were of analytical reagent grade and solutions were made up in triply-distilled water.The pulse radiolysis apparatus has been de~cribed.~ In the present work the necessary low doses and consequent low absorptions required the use of a long light path reaction cell.An internal reflection cell ' was used which has an effective length of 64 cm at 475 nm, the wavelength convenient for observing the thiocyanate transient absorption, and about 30 cm at 365 nm used for the iodide system. At these low doses (6-30 rad/pulse) and absorptions, 2389 Pulse radiolysis and flash photolysis of I-have established that the transient species with A , , , = 380 nm is the 1, ion formed by I+I+I, K ,As with (CNS); the value of K2 can be obtained using the equation,where D is the optical density due to I; at various concentrations of I-. Plots of this equation are given in fig. 6 and the values of K , in various conditions are collected

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The spectra due to electrons in alcohols at temperatures near their melting points show absorptions in the far and infra-red which, in general, decay to produce increased absorptions in the visible. At these temperatures the time for these changes increases in the order methanol, ethanol, n-butyl, isopropyl, n-propyl alcohol. For the latter the half-life of the absorption decay is given by T~ = A exp E/RT where log,,A = -15.7 and E = 25 kJ (5.9 kcal). Addition of solutes which react with electrons decreases the initial infra-red absorption and is interpreted as reaction with electrons before they become solvated. The observations are discussed in terms of molecular relaxation and electron migration.