Electron paramagnetic resonance (EPR), also known as electron spin resonance (ESR), is a spectroscopic technique used to study the properties of unpaired electrons in various systems. It is particularly useful for investigating the electronic structure and properties of paramagnetic species.
Paramagnetic species are those that possess unpaired electrons, which exhibit a magnetic moment due to their spin. In an applied magnetic field, the energy levels of these electrons split into different states, creating a spectrum of absorption or emission lines.
In EPR, a sample containing paramagnetic species is placed in a strong magnetic field and subjected to microwave radiation. The microwave radiation excites the unpaired electrons, causing transitions between different energy levels. By varying the magnetic field strength or the frequency of the microwave radiation, the absorption or emission of energy can be measured, providing valuable information about the electronic environment and properties of the paramagnetic species.
EPR spectroscopy is widely used in fields such as chemistry, physics, materials science, and biology to investigate a range of systems, including free radicals, transition metal ions, organic radicals, and defect centers in solids. It allows scientists to study the electronic structure, spin dynamics, and interactions of unpaired electrons, providing insights into chemical bonding, reaction mechanisms, and the behavior of materials at the atomic and molecular level.