How Does EPR work?
EPR is a magnetic resonance technique very similar to NMR (Nuclear Magnetic Resonance). However, instead of measuring the nuclear transitions in our sample, we are detecting the transitions of unpaired electrons in an applied magnetic field. Like a proton, the electron has spin, which gives it a magnetic property known as a magnetic moment. The magnetic moment makes the electron behave like a tiny bar magnet similar to one you might put on your refrigerator. When an external magnetic field is supplied, the paramagnetic electrons can either orient in a direction parallel or anti parallel to the direction of the magnetic field. This creates two distinct energy levels for the unpaired electrons and allows measurement of them as they are driven between the two levels. The microwave frequency radiation is applied to the sample from outside the microwave source. The microwave energy is absorbed when the magnetic field is equivalent to the energy differences between the two energy levels.
