Electron spin resonance description

The electron spin resonance (ESR) technique has been extensively used to study paramagnetic species that exist on various solid surfaces. These species may be supported metal ions, surface defects, or adsorbed molecules, ions, etc. Of course, each surface entity must have one or more unpaired electrons. In addition, other factors such as spin-spin interactions, the crystal field interaction, and the relaxation time will have a significant effect upon the spectrum. The extent of information obtainable from ESR data varies from a simple confirmation that an unknown paramagnetic species is present to a detailed description of the bonding and orientation of the surface complex. Of particular importance to the catalytic chemist... 

Matrix isolation-electron spin resonance. A third method used to measure HOz and ROz is matrix isolation with ESR (see earlier description of matrix isolation). Because HOz and ROz have distinct ESR signals, they can be differentiated (Mihelcic et al., 1985, 1990, 1993). For example, Fig. 11.53, part A, shows the ESR spectrum obtained when approximately... 

Eor more detail description of EPR, see, (a) A. Carrington and A. D. McLachlan, Introduction to Magnetic Resonance, Harper International, New York, 1967. (b) J. E. Wertz and J. R. Bolton, Electron Spin Resonance, McGraw-Hill, New York, 1972. 

Electron spin resonance (ESR) measures the absorption spectra associated with the energy states produced from the ground state by interaction with the magnetic field. This review deals with the theory of these states, their description by a spin Hamiltonian and the transitions between these states induced by electromagnetic radiation. The dynamics of these transitions (spin-lattice relaxation times, etc.) are not considered. Also omitted are discussions of other methods of measuring spin Hamiltonian parameters such as nuclear magnetic resonance (NMR) and electron nuclear double resonance (ENDOR), although results obtained by these methods are included in Sec. VI. 

To illustrate the technique we will consider a few examples of free radicals which have been prepared in the rotating cryostat. In particular phenyl and acetyl radicals and methyl-substituted allyl radicals are of interest as they have not been trapped previously or identified with certainty. Since electron spin resonance has been used extensively to detect and identify the free radicals, account of the results will inevitably involve some description and analysis of their spectra, but we wish to focus the main discussion on the conclusions that can be drawn about structure and reactivity of the radicals. For information about the principles of e.s.r. and the interpretation of the spectra of free radicals the reader is referred to review articles and books on the subject (Symons, 1963 Norman and Gilbert, 1967 Maki, 1967 Horsfield, 1967 Carrington and McLachlan, 1967 Ayscough, 1967 Carrington and Luckhurst, 1968). 

There are various kinds of spectroscopy visible and ultraviolet (UV) absorption spectroscopy, Raman and infrared spectroscopy, nuclear magnetic resonance spectroscopy, and electron-spin resonance (ESR) spectroscopy. A brief description of the principles of these techniques and their application to the study of ions in solution follows (see also Section 2.11). 

UV spectra usually involve electronic state transitions, so that simple Hartree-Fock and DFT calculations often are not sufficient PCM has been recently extended also to multi-configurational (MC-SCF) calculations [113] and to time-dependent approaches, allowing for the description of excited states and then the prediction of the so-called solvatochromic effects on these spectra. Nuclear magnetic resonance (NMR) and electron spin resonance (EPR) spectra are even more influenced by solute-solvent interactions moreover, the interpretation of experimental data is often very difficult without the support of reliable ab initio calculation, especially for EPR which is usually applied to unstable radical species. 

Materials characterization techniques, ie, atomic and molecular identification and analysis, are discussed in articles the tides of which, for the most part, are descriptive of the analytical method. For example, both infrared (ir) and near infrared analysis (nira) are described in Infrared and raman SPECTROSCOPY. Nudear magnetic resonance (nmr) and electron spin resonance (esr) are discussed in Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed in Spectroscopy (see also Chemh.itmtnescence Electro-analytical technique Immunoassay ZvIass spectrometry Microscopy Microwave technology. Plasma technology and X-ray technology). 

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