Electron paramagnetic resonance (EPR) is a spectroscopic technique used to study materials with unpaired electrons. It detects the magnetic properties of these electrons when they are exposed to a magnetic field and microwave radiation. EPR is particularly useful for investigating free radicals, transition metal complexes, and defects in solids. The technique provides information about the electronic structure and dynamics of paramagnetic species. By analyzing the resulting spectra, researchers can gain insights into molecular interactions, reaction mechanisms, and the environment surrounding the unpaired electrons, making EPR valuable in fields like chemistry, biology, and materials science.