The Case of Two or More Unpaired Electrons Fine Structure

The Case of Two or More Unpaired Electrons Fine Structure 

The first problem (i) can usually be avoided by using a lower concentration of radical ions, but mechanisms (ii) and (in) are sometimes unavoidable. Also, since useful information may often be obtained by a study of radicals trapped in pairs in crystals or in powders, the nature of the interaction between them will be briefly considered here. 

Since nearest neighbor metal ions in a crystal lattice are usually separated by at least a few Angstroms (very seldom less than 5 A), the interaction between an electron on each metal ion is represented quite well to a first-order approximation by a simple classical dipolar interaction between electrons located at a point on each metal atom. The splitting AH produced by this spin-spin interaction is given by 

This approach breaks down completely if there is appreciable de-localization of the unpaired electron onto the ligands, since r would take a wide range of values, producing a splitting spread over a wide range, and yielding very broad lines. 

When there is an interaction between an unpaired electron and a magnetic nucleus, hyperfine structure may be detected. Different spectra are obtained when an isolated pair of ions, each with S = and 7=1 is allowed to interact under different conditions. A single ion would give 

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