3596
FREDP. ABRAMSON AND RICHARD F. FIRESTONE
Combined Effects of Dose Rate and Temperature in the Radiolysis of Liquid Chloroform. Application of Homogeneous Kinetics to the Radiolytic System1
by Fred P. Abramson2and Richard F. Firestone* Department of Chemistry, The Ohio State University, Columbus, Ohio 43210
(Received June 16, 1966)
The effects of dose rate and temperature on the 100-ev yields of the major radiolysis products of pure air-free liquid CHCL have been determined in the vicinity of 1 Mrad/hr at temperatures between -57 and 63". Qualitative effects of dose rate variations are found to be in accord with expectations based on a homogeneous free-radical mechanism and do not derive from track-track overlap. Numerical solutions of the steady-state equations for the major organic free-radical intermediates (CHC12. and CC13.) are shown to be quantitatively consistent with the proposed homogeneous free-radical mechanism between 0 and 63" if spur reactions are assumed to function independently of the homogeneous mechanism. The form of the numerical solutions provides a basis for explaining effects of dose rate up to lo4 iliradslhr at 25". The rate constant for the reaction, CHClz. CHCl3 + CHZC12 CCh-, is evaluated at 0, 26, 48, and 63" and is shown to be represented by k = 1.6 X 10-l6 e-67mlRT cc/molecule sec in liquid CHC13.
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Introduction The radiolytic decomposition of pure air-free liquid CHC1, is singularly interesting because of its marked sensitivity to temperature from -62 to 6304 and to dose rate variations over an extremely wide range from less than 0.1 to greater than 104'Mrads/hr.696 The effects of temperature and of several solutes upon the rates of formation of the major products have established the predominantly free-radical character of the mechanism and the identities of the most abundant thermal free-radical intermediates in the liquid phase.4 This article reports results of a careful investigation of the combined effects of dose rate and temperature in the vicinity of 1 Mrad/hr and between -57 and 63". Certain rigorous tests of the proposed mechanism are provided by numerical solutions of the steady-state equations for CHClz and CC13 radicals in the 0 to 63" region. Experimental Section Mallinckrodt AR chloroform was washed with successive batches of distilled water to remove ethanol added by the manufacturer as a stabilizer to a level below the limit of detectability by gas chromatography (
