Effect of temperature on the early stages of radiolysis. Part 1.—Pulse radiolysis of alkaline aqueous solutions between 300 and 77 K

Abstract

λ_max for the spectrum of hydrated electrons in 10 M alkaline solution shows a monotonic blue shift from 680 nm at 300 K to 585 nm at 140 K below which no further change occurs. G(e^–_s)ε measured immediately after a 0.2 µs pulse of 3 meV electrons increases by about 50 % as T decreases from 300 to 220 K, then sharply decreases by about 40 % of this maximum value as T falls from 220 to 140 K, thereafter remaining constant to 77 K. Added nitrite, nitrate or chromate ions reduce G(e^–_s)ε at all temperatures in a manner suggesting a simple competition between solute and potential traps for mobile electrons. The decay of the electrons has a faster component which becomes slower and more pronounced as T falls and accounts entirely for the increase of G(e^–_s)ε as T falls from 300 K to 220 K, when the order of this decay changes from first towards second. Spectral shape changes indicate that “red” electrons can be mobilized more easily than “blue” electrons but that retrapping is less probable the lower the temperature. The first- and second-order rate constants for solute-free and solute-containing systems all fit the equation ln k= constant–(6.8 ± 0.6 kJ)/R(T–135 ). These and related data are interpreted in terms of a spur model and diffusion controlled processes with 135 K as the temperature below which these systems can be regarded as entirely rigid.