The Pulse Radiolysis of Dimethylsulfoxide and Binary Mixtures with Water

Abstract

The simultaneous interaction of solvated electrons with strongly solvating water molecules and weakly solvating dimethylsulfoxide (DMSO) molecules has been studied by pulse radiolysis. In all DMSO/H2O mixtures investigated the solvated electrons have a single absorption band with a maximum intermediate between that of pure DMSO (λmax > 1500 nm) and that of water (λmax = 720 nm). There is a nearly linear relationship between the photon energy of λmax and the bulk dielectric constant, indicating that the optical properties of solvated electrons in the mixtures are not dominated by the water. A minimum is observed in the variation of Gεmax with DMSO/H2O composition which may be associated with intermolecular structure. In mixtures containing > 0.2 mole fraction DMSO the solvated electrons have half-lives of 11–18 ns.The radiation produced oxidizing species in DMSO has a half-life of 1–4 µs and an absorption band centered at 600 nm. This species seems to be present in all DMSO/H2O mixtures.Pure DMSO gives a free-ion yield in the range 1.2 to 1.8, as determined separately for the oxidizing and reducing species by bromide and anthracene scavenging experiments respectively. This free-ion yield is in keeping with the dielectric constant of DMSO of 46. The yields in fully deuterated DMSO are ~30% higher than in the protonated material.