Electron paramagnetic resonance (EPR), also known as electron spin resonance (ESR) and electron magnetic resonance (EMR), is the name given to the process of resonant absorption of microwave radiation by paramagnetic ions or molecules, with at least one unpaired electron spin, and in the presence of a static magnetic field. EPR was discovered by Zavoisky in 1944. It has a wide range of applications in chemistry, physics, biology, and medicine: it may be used to probe the "static" structure of solid and liquid systems, and is also very useful in investigating dynamic processes.
The most commonly used EPR spectrometer is in the range of 9-10 GHz (X-band). However, advances in electronics have facilitated the development of spectrometers working at frequencies ranging from several hundred MHz to several hundred GHz.
The EPR Lab currently maintains EPR spectrometers working at 8-10 GHZ (X-Band) and 35 GHz (Q-band).
Multifrequency EPR (1 GHz to 100 GHz) provides an experimental route to study the magnetic interactions in paramagnetic materials. The elucidation of parameters like g, A, D, E, and Q, which characterize these interactions, can lead to an understanding of atomic and molecular structure at magnetic sites. High sensitivity and the ability to investigate small-scale order in powders, polymers, and frozen solutions are key advantages of EPR over a wide frequency range. Additional techniques employing both EPR and NMR methods (ENDOR - electron-nuclear double resonance, that are available at the EPR Lab extend the precision and scope of such investigations. EPR spectroscopy, combined with techniques such as spin trapping, can be used to detect and follow free radical reactions in biological systems.
Low-frequency EPR spectrometers and special microwave detectors and circuitry provide the capability to obtain spectra from living animals and perfused organs, including the concentration of oxygen in tissues, redox metabolism, distribution of spin-labeled molecules, and biophysical measurement. Special materials developed and being improved at the IERC provide sensitive EPR probes of both oxygen and nitric oxide (NO) in tissues.
Weil and Bolton, Electron Spin Resonance; Elementary Theory and Piratical Applications, 2nd Edition(2007).
Abragam and Bleaney, Electron Paramagnetic Resonance of Transition Ions (1970).
Pilbrow, Transition Ion Electron Paramagnetic Resonance (1990).