Rate constant and arrhenius parameter determination for the reaction of the hydrated electron with iodomethane, iodoethane, 1-iodopropane and 2-iodopropane in aqueous solution

The techniques of electron pulse radiolysis and absorption spectroscopy have been used to directly measure rate constants for the hydrated electron reaction with CH3I, C2H5I, 1-C3H7I and 2-C3H7I. At 25°C, specific values of (1.78 ± 0.05) ×x 1010, (1.57 ± 0.07) × 1010, (1.05 ± 0.06) × 1010 and (1.05 ± 0.03) × 1010 dm3 mol−1 s−1 were determined for these compounds respectively, with corresponding overall activation energiesof 16.9 ± 1.3 (3.2–35.5°C), 19.5 ± 1.1 (3.3–51.6°C), 16.60 ± 0.65 (2.5–85.1°C) and 12.94 ± 0.44 (2.5–84.5°C) kJ mol−1. The slight curvature observed in the Arrhenius plots for the three larger iodoalkanes suggests that these rate constants are influenced by both diffusion and chemical processes. By fitting the measured temperature-dependent rate constants to the general equation 1/kobs = 1 /kdiff + 1/kreact, where kobs, is the measured rate constant, kdiff is the encounter rate constant of the two reacting species and kreact is the rate constant that would be measured if diffusion of the species was not rate influencing, specific Arrhenius parameters for only the chemical component have also been determined.