Basic Principles of Electron Spin Resonance

Abstract

The technique of electron spin resonance may be regarded as a fascinating extension of the Stern-Gerlach experiment. In one of the most fundamental experiments on the structure of matter, Stern and Gerlach showed that an atom with a net electron magnetic moment can take up only discrete orientations in a magnetic field. Subsequently, Uhlenbeck and Goudsmit linked the electron magnetic moment with the radical idea of electron spin. Whether or not the reader has an immediate interest in the multitude of systems to which the technique is applicable, he can ill afford to ignore the insights which it can provide. Further, there is hardly another application from which one can gain a clearer insight into many of the fundamental concepts of quantum mechanics. Much of our knowledge of the structure of molecules has been obtained from the analysis of molecular absorption spectra. Such spectra are obtained by measuring the attenuation vs. wavelength (or frequency) of a beam of electromagnetic radiation as it passes though a sample of matter. Lines or each line or band measures the energy separation of two levels. Given enough data and some guidance from theory, one may construct an energy-level diagram from a spectrum.