Pulse Radiolysis Studies. XVIII. Spectrum of the Solvated Electron in the Systems Ethylenediamine–Water and Ammonia–Water

Abstract

The pulse radiolysis technique with fast infrared detection was used to determine the optical absorption spectrum of the solvated electron in the systems ethylenediamine–water and ammonia–water. These spectra, determined over the entire concentration range, show the following: In ammonia and in ethylenedamine, the bands at 1550 and 1350 nm, respectively, have the same shape and position as those attributed to the solvated electron in alkali metal solutions. In each of the two-component systems a single band is seen with the peak position intermediate to those in the pure solvents. For ethylenediamine–water mixtures, the band shape (normalized) and half-width (energy scale) are invariant with composition, while for ammonia–water mixtures the ratio of the peak position to the half-width is invariant. These observations suggest a delocalized electron with optical characteristics determined by the aggregate properties of the solvent. Models which require that the optical properties be strongly influenced by solvation with a small number of solvent molecules are not in accord with these observations. Kinetic data indicate that the decay of the solvated electron in ammonia and in ethylenediamine is a complex process. The rate constant for the reaction of the solvated electron in ammonia with ammonium ion was found to be at least four orders of magnitude lower than the diffusion-controlled limit.