Electron Spin Resonance - Basic Concepts

Electron s m resonance involving traimtions between the Zeeman levels is achieved by applying electromagnetic radiation of frequency cOq such that AE = hcoo-The resonance condition is then satisfied 

ESR spectroscopy was mainly developed to study the interaction energies of a parmagnetic atom in a constant magnetic field. It has therefore been mainly used to characterise rather than identify paramagnetic species. ESR has been used in polymer studies to identify the radical species generated by various processes, to determine the number of radicals produced and to follow the decay of radicals with time and environment. 

Since polymers are covalently bonded molecules formed from elements in the first two periods of the periodic table, all the electrons in the molecule are paired and there is no resultant magnetic moment. It is necessary to break covalent bonds to obtain unpaired electrons, before ESR spectroscopy can applfed. ESR thus provides information on the number and site of the broken bond. 

The three major limitations on the application of ESR to the general study of fracture in polymers concern, 

Glass insert arrangement for low temperature operation in standard cavity of Varian E-9 spectrometer 

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The course of chemical reactions in irradiated proteins is determined hy factors that influence the reactivity of the primary free radicals, the kind of protein radicals formed, and the decay of these protein radicals to stable products. To understand these reactions, basic radiation chemical concepts are considered, chemical changes in several representative proteins irradiated under different conditions are compared, and results from optical and electron spin resonance studies on model systems are presented. Among the reactions described are those involving cation, anion, and a-carbon radicals of amino acids and peptides. Analogous reactions common to proteins are then summarized. These mechanistic considerations have important implications for the irradiation of hydrated muscle proteins at — 40°C and for radiation sterilization of foods. 

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. 

However, mathematically speaking, the wave functions can be orthogonal, but in the physical space, this conception impeded an unfeasibility for electron transitions between the states. The decomposition of V(n) into non-combining (orthogonal) spaces was possible only if spin resonance was taken as a kind of perturbation. Its basic structure could be analyzed even at the level of the unperturbed system without spin. 

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