What is EPR spectroscopy

Electron paramagnetic resonance (EPR) spectroscopy is a resonance technique involving microwave-induced transitions between magnetic energy levels of electrons which possess a net spin and orbital angular momentum. An EPR spectrum provides information about paramagnetic species. 

Electron paramagnetic resonance (EPR) spectroscopy (also called electron spin resonance (ESR) spectroscopy), is used to study paramagnetic species with one or more unpaired electrons, e.g. free radicals, diradicals, metal complexes containing paramagnetic metal centres, defects in semiconductors and irradiation effects in solids. While diamagnetic materials are EPR silent, paramagnetic species always exhibit an EPR spectrum. This consists of one or more lines, depending on the interactions between the unpaired electron (which acts as a probe ) and the molecular framework in which it is located. Analysis of the shape of the EPR spectrum (the number and positions of EPR lines, their intensities and line widths) provides information 

EPR spectroscopic measurements can be performed at high, room or low ( 4K) temperature. Samples may be solid (single crystal or powder) or liquid (fluid or frozen solution, a glass ). In this introduction to EPR spectroscopy, we shall be concerned (Mily with magnetically dilute systems in which the unpaired electrons are involved in intramolecular (not intermolecular) interactions. We shall focus attention on the application of the technique to mononuclear, metal-containing systems. 

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