Recent Applications of Electron Spin Resonance in Chemistry

Abstract

Free radicals, which are molecular fragments having odd, unpaired electrons, may be detected by observing transitions between the energy states corresponding to the parallel and anti-parallel orientations of the unpaired electron in a magnetic field. This is the technique of Electron Spin Resonance. Interaction of the unpaired electron with other magnetic nuclei in the radical, such as protons, produces e. s.r. spectra having considerable hyperfine structure. Analysis of the hyperfine structure often allows identification of the radical and gives information about the unpaired spin density distribution. The study of oriented radicals, trapped in the lattices of single crystals, gives additional information about their structure. Electron resonance has been used to investigate free radicals produced by the photolysis of chemical systems by visible and ultra-violet radiation, particularly in low temperature glasses. Occluded radicals and high energy radiation damage in polymers have been studied. The technique has also been applied to kinetic measurements involving shortlived free radicals. Examples illustrating these applications of e. s. r. in chemistry are discussed.