- © 2014 Mineralogical Society of America
Electron paramagnetic resonance (EPR) spectroscopy, also known as electron spin resonance (ESR) spectroscopy, is a group of techniques used to study paramagnetic species that contain one or more unpaired electrons. The basic principles of EPR are analogous to those of nuclear magnetic resonance (NMR) spectroscopy, because they both deal with interactions between electromagnetic radiation and magnetic moments. However, the former is based on the excitation of electron spins, whereas nuclear spins are excited in the latter. EPR as a structural probe provides a wealth of information about the local structures and dynamic processes of the paramagnetic species studied, and is known for its unique sensitivity (~1012 spins/cm3 or parts per billion; Pan et al. 2002a; Weil and Bolton 2007), unmatched by any other structural techniques. In addition, quantitative EPR, provided that sufficient calibration and standardization are carried out, is possible and is useful for chemical analysis, dosimetry and geochronology, with applications to not only rocks and minerals but also other Earth and planetary materials such as coals, crude oils and meteorites (Ikeya 1993; Dyrek et al. 1996, 2003; Eaton et al. 2009).
The basic principles of EPR spectroscopy can be found in various textbooks and monographs (Abragam and Bleaney 1970; Poole and Farah 1999; Schweiger and Jeschke 2001; Weil and Bolton 2007; Brustolon and Giamello 2009; Eaton et al. 2009; Misra 2011). Excellent reviews with emphasis on applications of EPR spectroscopy to minerals can be found in Marfunin (1979), Calas (1988), Vassilikou-Dova (1993), and Goodman and Hall (1994). However, most previous reviews on applications to minerals focused almost exclusively on conventional continuous-wave (CW) techniques, whereas more advanced techniques such as pulse electron nuclear double resonance (ENDOR) and electron spin echo envelope modulation (ESEEM) …