Effect of Temperature on the Reactions of Electrons during the γ Radiolysis of Liquid n-Propanol

Abstract

Purified n-propanol was irradiated at temperatures from − 120° to + 264° and G(H2) increased from 4.1 to 5.9 over this range. Solutions of electron scavengers (acid and nitrous oxide) were irradiated at − 120°, + 25°, and 140°. The values of G(H2) for absolutely pure n-propanol were estimated to be 4.3 at − 120°, 4.9 at 25°, and 6.0 at 140°. The value of G(total ionization) ≈ 4.3 estimated at − 120° was assumed to be independent of temperature. The free-ion yield was G(esolv−)fi = 1.1 at − 120°, 1.2 at + 25°, and 0.8 at 140°. A reaction mechanism was proposed and the measured hydrogen and nitrogen yields were subjected to kinetic analysis; homogeneous kinetics were used for the reactions of the free ions and nonhomogeneous kinetics were used for the reactions in spurs. The activation energy of dielectric relaxation (6.1 kcal/mole) is greater than that of diffusion (∼ 4.5 kcal/mole); it was necessary to use a time-averaged value of the dielectric constant for the smaller ion–electron separation distances at − 120°, but the static value was satisfactory elsewhere. The reaction esolv−→→n-C3H7Osolv− + H has a rate constant of about 5 × 105 sec−1 at 25° and has an activation energy of 4.5 kcal/mole and an entropy of activation of − 19 cal/deg·mole. Only a fraction of the electrons that undergo geminate neutralization lead to hydrogen formation; the value of the fraction is 0.29 at − 120°, 0.52 at + 25°, and 0.63 at 140°.