Optical spectra and yields of solvated electrons and metal-electron species in alkali metal systems

Abstract

The effect of solvent on the optical spectra of solvated electrons, e^–_s, cation-electron aggregates, (M⁺, e^–_s), and alkali metal anions, M^–, is discussed for a variety of alkali metal systems. With increasing solvent polarity the optical band maxima shift toward the blue with the solvent dependence decreasing significantly in the order (M⁺, e^–_s) > e^–_s > M^–. The relative differences are interpreted in terms of ion-pairing and cation solvation. In ethylamine + ammonia mixtures only the e^–_s band exhibits a pronounced dependence on solvent composition consistent with preferential solvation by NH₃ molecules.

Initial yields of e^–_s measured by pulse radiolysis in methylamine (MA), ethylamine (EA) and isopropylamine (IPA) correspond to G(e^–_s)∼ 2, whereas the fraction of electrons escaping the spur decreases markedly in the order MA > EA > IPA. The results indicate that the decay processes for e^–_s in MA (and NH₃) are slow compared with the rate of diffusion. In EA and IPA the decay is markedly temperature dependent and at temperatures approaching the freezing point is comparable with that in MA. This leads to an escaped yield approaching that observed for MA.