Electron-spin resonance with electrochemistry

Electrochemistry, organic, structure and mechanism in, 12, 1 Electrode processes, physical parameters for the control of, 10, 155 Electron donor-acceptor complexes, electron transfer in the thermal and photochemical activation of, in organic and organometallic reactions. 29, 185 Electron spin resonance, identification of organic free radicals, 1, 284 Electron spin resonance, studies of short-lived organic radicals, 5, 23 Electron storage and transfer in organic redox systems with multiple electrophores, 28, 1 Electron transfer, 35, 117... 

In addition to UV-vis absorption measurements, other spectroscopic techniques can be used for monitoring the dynamics of electrochemical events or the fate of electrogenerated species. Earticularly informative are the couplings of electrochemistry with electron spin resonance, nuclear magnetic resonance, and mass spectroscopy. A variety of specially designed cells have been con-... 

Many types of spectroscopy have been coupled with electrochemistry including electronic absorption spectroscopy, X ray (see X-Ray Absorption Spectroscopy), infrared (IR) (see Vibrational Spectroscopy), or Raman spectroscopy, eUipsometry, specular reflectance, and electron spin resonance (ESR). Electronic absorption spectroscopy, one of the most prominent electrochemistry coupled with spectro-electrochemical techniques, will be discussed here as will... 

Electron spin resonance (ESR, also known as electron paramagnetic resonance, EPR) is used for the detection and identification of electrogenerated products or intermediates that contain an odd number of electrons that is, radicals, radical ions, and certain transition metal species. Because ESR spectroscopy is a very sensitive technique, allowing detection of radical ions at about the 10 M level under favorable circumstances, and because it produces information-rich, distinctive, and easily interpretable spectra, it has found extensive application to electrochemistry, especially in studies of aromatic compounds in nonaqueous solutions. Also, electrochemical methods are particularly convenient for the generation of radical ions thus they have been used frequently by ESR spectroscopists for the preparation of samples for study. Several reviews dealing with the principles of ESR and the application to electrochemical investigations have appeared (134-138). 

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. 

ESR spectroscopy is a sensitive detection method designed to provide information on radicals. This method, also known as electron paramagnetic resonance (EPR) spectroscopy, is naturally a good choice for coupling to electrochemistry as radicals can easily be electrogenerated. ESR involves the detection of unpaired electrons which are affected by nearby nuclei. Radical spin states are modified by interaction with a magnetic field, equation (17). ... 

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