electron paramagnetic resonance (EPR)

Electron paramagnetic resonance (EPR) and/or electron spin resonance (ESR) is defined as the form of spectroscopy concerned with microwave-induced transitions between magnetic energy levels of electrons having a net spin and orbital angular momentum. The term electron paramagnetic resonance and the symbol EPR are preferred and should be used for primary indexing.
PAC, 1989, 61, 2195. 'Recommendation for EPR/ESR nomenclature and conventions for presenting experimental data in publications (Recommendations 1989)' on page 2196 (https://doi.org/10.1351/pac198961122195)