Electron spin resonance basic principle

Schwelger A 1991 Pulsed electron spin resonance spectroscopy basic principles, techniques, and examples of applications Angew. Chem. Int. Edn Engl. 30 265-92... 

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... 

Understand the basic principles of electron spin resonance and the information that this technique provides about free radical structure... 

To place these developments in perspective, some account will be given of the invention of magnetic resonance methods for condensed matter and of the various types of apparatus that were available, especially for MR where there has been substantial improvement in instrumentation with time. (We shall abbreviate nuclear magnetic resonance by NMR" and electron paramagnetic resonance by "EPR". We prefer the latter designation to electron spin resonance, because electron orbital as well as spin moments may be involved.) Since many readers may not be familiar with the principles of magnetic resonance, qualitative explanations of basic aspects are included. Emphasis will be on work in the United States, but some contributions from elsewhere will be mentioned. 

It does not seem necessary or advisable to describe once again the basic principles of electron spin resonance, since there are now available a substantial number of reviews and books dealing with these matters. Introductory articles have been written by Carrington S and Atherton S and there exist several text books S " s which treat the subject on a more quantitative level. Electron spin resonance papers have been regularly reviewed in the Chemical Society of London s Annual Reports and these articles may be used as guides to the more significant aspects of current developments in the field. Three features of an electron spin resonance spectrum are of interest the hyperfine splitting constants of any nuclei with non-zero spin in the molecule, the g-factor of the radical, and the widths of the various lines in the spectrum. 

Line-width effects in electron spin resonance spectra have been the subject of three recent reviews " and so there seems little point in further detailed repetition of the principles at this time. Basically, line-width effects will be observed when the Hamiltonian describing the spin systems contains time-dependent elements having frequency components comparable to frequency separations in the spectrum. The mechanisms... 

Pulsed Electron Spin Resonance Spectroscopy Basic Principles, Techniques and Examples of Application by A. Schweiger, Angew. Chem., Int. Ed. (1991) 30, 265. 

This chapter is intended to recall the principles of magnetism, the definition of magnetic induction and of magnetic induction in a vacuum which is referred to as magnetic field. Readers may not recollect that the molar magnetic susceptibility is expressed in cubic meters per mol Some properties of electron and nuclear spins are reviewed and finally some basic concepts of the magnetic resonance experiments are refreshed. In summary, this chapter should introduce the readers into the language used by the authors. 

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