ABSTRACT
This chapter focuses on the instrumental and experimental aspects of Electron paramagnetic resonance (EPR). EPR is a technique for measuring the absorption of electromagnetic radiation by a sample with unpaired electron spins. The EPR signal from a sample is proportional to the microwave magnetic susceptibility, which has real and imaginary components. A pulsed EPR experiment measures the response of the electron spins after a sequence of one or more pulses of microwaves. Irradiation with a second frequency during an EPR experiment can provide much more detailed information about the spin system than can the usual single-frequency measurement. Electron–electron spin–spin coupling can lead to resolved splitting in EPR spectra just as can electron–nuclear coupling in EPR and nuclear–nuclear coupling in Nuclear magnetic resonance (NMR). The magnetic field homogeneity requirements are not as demanding for EPR as for NMR, since EPR linewidths are usually rather large in comparison with NMR linewidths.
