Electron spin resonance spectroscopy fundamentals

Spectroelectrochemistry encompasses a group of techniques that allow simultaneous acquisition of electrochemical and spectroscopic information in situ in an electrochemical cell. A wide range of spectroscopic techniques may be combined with electrochemistry, including electronic (UV-visible) absorption and reflectance spectroscopy, luminescence spectroscopy, infrared and Raman spectroscopies, electron spin resonance spectroscopy and ellipsometry. Molecular properties such as molar absorption coefficients, vibrational absorption frequencies and electronic or magnetic resonance frequencies, in addition to electrical parameters such as current, voltage or charge, are now being used routinely for the study of electron transfer reaction pathways and the fundamental molecular states at interfaces. In this article the principles and practice of electronic spectroelectrochemistry are introduced. 

Progress in photochemistry could only be made following progress in spectroscopy and, in particular, the interpretation of spectra in at least semiquantitative terms, but history has shown that this was not enough. The arrival of new methods of analysis which permit determination of small amounts of products, the development of flash photolysis, nuclear magnetic resonance, and electron spin resonances which can yield valuable information about the natures of intermediate excited states, as well as of atoms and radicals, all have permitted the photochemist to approach the truly fundamental problem of photochemistry What is the detailed history of a molecule which absorbs radiation ... 

This volume covers a wide range of fundamental topics in coal maceral science that varies from the biological origin of macerals to their chemical reactivity. Several chapters report novel applications of instrumental techniques for maceral characterization. These new approaches include solid l3C NMR, electron spin resonance, IR spectroscopy, fluorescence microscopy, and mass spectrometry. A recently developed method for maceral separation is also presented many of the new instrumental approaches have been applied to macerals separated by this new method. The contributions in this volume present a sampling of the new directions being taken in the study of coal macerals to further our knowledge of coal petrology and coal chemistry. 

Very primary events in the chemical effect of radiations on matter are excitation and ionization of molecules, which result in the formation of neutral free radicals and radical ions. These reactive species play vital roles in the radiation-induced chemical reactions. As they are paramagnetic with an unpaired electron, electron spin resonance (ESR) spectroscopy has been a useful method for elucidating the mechanism of radiation-induced reactions in solid matter where radical species can be trapped temporarily. Since the early days of the chemical application of ESR, this method has been applied very often to the identification and quantification of free radicals in polymers irradiated by radiation [1]. This is probably because, from the view-point of fundamental research, a variety of free radicals are readily trapped in solid polymers and, from the view-point of applied research, these free radicals have close correlation with radiation-induced crosslinking and degradation of polymers. 

The electronic g-tensor is a fundamental quantity in electron spin resonance (ESR) spectroscopy. Its experimental reading is based on the assumption that the following equation is fulfilled... 

It is not necessary to deal with these techniques in detail here, since there are several books and monographs on the subject. The fundamental theory and practice of electrochemical and spectroelectrochemical methods can be found in [1,2] and also in [3-5], where investigations of polymeric surface layers are emphasized. Excellent monographs on EQCM [6-9] and PBD [10] are also recommended for further studies. Infrared, Mdssbauer spectroscopy, ellipsometry, etc., are described in [I I], while electron spin resonance is discussed in [12], radiotracer in [13], scanning tunneling microscopy in [14], and scanning electrochemical microscopy in [15]. The fundamentals of electrochemical impedance spectroscopy are treated in [1,2,16] however, the different models elaborated for electrochemically active films and membranes can be found in various papers (see later), while the most important methods for analyzing impedance spectra, as reported before 1994, are well summarized in [3]. Nevertheless, the essential elements of these techniques are briefly discussed here, in order to help the reader to understand the experimental material presented in this book. 

The main purpose of this book is to collect the present available information on the applications of electron spin resonance (ESR) spectroscopy in polymer research. The book has been written both for those who want an introduction to this field, and for those who are already familiar with ESR and are interested in application to polymers. Therefore, the fundamental prin-dples of ESR spedroscopy are first outlined, the experimental methods including computer applications are described in more detail, and the main emphasis is onthe application of ESR methods to polymer problems. The authors hope that this book will provide a useful source of information by giving a coherent treatment and extensive references to original papers, reviews, and discussions in monographs and books. In this way we hope to encourage polymer chemists, organic chemists, biochemists, physicists, and material scientists to apply ESR methods to their research problems. (2519 references). 

Spectroscopy. Microwave radiation is used for electron paramagnetic resonance, also known as electron spin resonance, analysis, which has been crucial in the development of the most fundamental theories in physics, including quantum mechanics, the special and general theories of relativity, and quantum electrodynamics. Microwave spectroscopy is an essential tool for the development of scientific understanding of electromagnetic and nuclear forces. 

A major limitation for NMR spectroscopy is the intrinsically low sensitivity due to the rather unfavorable Boltzmann distribution for nuclear spins at thermal equilibrium. Thus, considerable effort in magnetic resonance spectroscopy is made towards sensitivity enhancement by hyperpolarization techniques, such as optical polarization, para-hydrogen-induced polarization enhancement, and dynamic nuclear polarization (DNP), a method which exploits the magnetization of unpaired electrons in stable radicals or transition metals to enhance nuclear polarization beyond the Boltzmann limit. In the chapter Dynamic Nuclear Hyperpolarization in Liquids, the fundamental theory for different polarization transfer... 

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