Electron Paramagnetic Resonance ( EPR ) Spectroscopy

Abstract Electron‐Paramagnetic Resonance (EPR) spectroscopy, also know as Electron‐Spin Resonance (ESR) spectroscopy, monitors the energy levels of paramagnetic molecules. The major energy interaction (Zeeman Interaction) is between the magnetic moment of the electron and the field of a large uniform magnet. This interaction splits the normally degenerate spin levels of the electron and the electron‐paramagnetic resonance (EPR) spectrometer measures the energy of this interaction. The EPR spectrometer is described along with a discussion of spectral optimization techniques. Additionally, energy interaction terms are described and include hyperfine coupling (the interaction of the magnetic moments of the unpaired electron and magnetic nuclei) and spin‐orbit coupling, which influences the magnitude of the spectroscopic g ‐factor and the energy levels of S > 1/2 systems. The general features of half‐integer and integer high‐spin systems are further described, including examples.