Introduction to Electron Paramagnetic Resonance
(EPR) Spectroscopy

The extended field of (Electron Paramagnetic Resonance (EPR)) spectroscopy can be regarded as a valuable tool for chemistry, physics, biology, biochemistry and related fields of research. EPR methods can - in principle - be applied to investigate all systems and processes in which unpaired electron spins are present. Thus, they are alternatively called EPR (Electron Spin Resonance) methods. Some examples of what can be done by EPR spectroscopy:

• determination of structural properties on a molecular scale
• investigation of molecular dynamics in solutions and solids
• selective characterization of redox-active centers in proteins
• study of kinetics of chemical reactions

• g-tensors,
• electron-spin electron-spin interactions (finestructure),
• electron-spin nuclear-spin couplings (hyperfine structure),
• nuclear quadrupole coupling (NQR) parameters,
• spin-lattice and spin-spin relaxation rates.

The area of EPR developed rapidly. The story began with the basic cw-EPR (continuous wave) experiment first realized in 1944. First cw-ENDOR (elctron nuclear double resonance) methods at X-band (9 GHz) frequencies were realised during the 1950's. Then the extended field of pulsed spin echo, ESEEM (electron spin echo envelope modulation) and FT-EPR (Fourier transform) methods was entered - a process being still in progress. A new focus occured only quite recently: the realisation of high frequency EPR experiments in very high magnetic fields using superconducting magnets.
Since 2000 our group operates one of the very few home-built pulsed (180 GHz) high-field EPR machines. Both pulsed EPR as well as cw-EPR experiments can be performed on this machine.
Instead of repeating what other people already put on the web, below some selected links to introduce EPR methods:

EPR links

An informative overview by the group of Prof. Dr. G. Jeschke at the ETH Zürich in Switzerland: What is EPR
Wikipedia EPR (english)
Wikipedia EPR (deutsch)