Experimental techniques electron paramagnetic resonance

Electron spin is the basis of the experimental technique called electron paramagnetic resonance (EPR), which is used to study the structures and motions of molecules and ions that have unpaired electrons. This technique is based on detecting the energy needed to flip an electron between its two spin orientations. Like Stern and Gerlach s experiment, it works only with ions or molecules that have an unpaired electron. 

Up to date, several experimental techniques have been developed which are capable of detecting some of these particles under ordinary thermodynamic conditions. One can use these methods to keep track of transformations of the particles. For instance, it is relevant to mention here the method of electron paramagnetic resonance (EPR) with sensitivity of about 10 particles per cm [IJ. However, the above sensitivity is not sufficient to study physical and chemical processes developing in gaseous and liquid media (especially at the interface with solids). Moreover, this approach is not suitable if one is faced with detection of particles possessing the highest chemical activity, namely, free radicals and atoms. As for the detection of excited molecular or atom particles... 

Electron paramagnetic resonance (EPR) and NMR spectroscopy are quite similar in their basic principles and in experimental techniques. They detect different phenomena and thus yield different information. The major use of EPR spectroscopy is in the detection of free radicals which are uniquely characterised by their magnetic moment that arises from the presence of an unpaired electron. Measurement of a magnetic property of a material containing free radicals, like its magnetic susceptibility, provides the concentration of free radicals, but it lacks sensitivity and cannot reveal the structure of the radicals. Electron paramagnetic resonance spectroscopy is essentially free from these defects. 

For decades, there have been voluble and passionate arguments in favor of using each of the terms electron paramagnetic resonance (EPR) and electron spin resonance (ESR) to describe a single experimental technique. A group of scientists has banded together to form the International EPR... 

Experimental Techniques A absorption CIMS = chemical ionization mass spectroscopy CK = competitive kinetics DF discharge flow EPR = electron paramagnetic resonance FP = flash photolysis FT = flow tube FTIR Fourier transform intra-red GC = gas chromatography, UF = laser induced fluorescence LMR = laser magnetic resonance MS = mass spectroscopy PLP = pulsed laser photolysis SC = smog chamber SP = steady (continuous) photolysis UVF = ultraviolet flourescence spectroscopy... 

Electron paramagnetic resonance (EPR) is also a technique whereby the local structure of an impurity ion may be inferred by correlating the geometry with the experimentally determined electronic properties of the center. The third order expression for the g values can be written in terms of the Jahn-Teller angular coordinate as... 

This review article is concerned with the structure, bonding, and dynamic processes of water molecules in crystalline solid hydrates. The most important experimental techniques in this field are structural analyses by both X-ray and neutron diffraction as well as infrared and Raman spectroscopic measurements. However, nuclear magnetic resonance, inelastic and quasi elastic neutron scattering, and certain less frequently used techniques, such as nuclear quadrupole resonance, electron paramagnetic resonance, and conductivity and permittivity measurements, are also relevant to solid hydrate research. 

The examples chosen here have emphasized the use of H NMR. However, other nuclei can be examined, including C, and O. Thus, in the case of ligand exchange processes involving acetonitrile, one can use C NMR with an isotope-enriched sample [G4]. In addition, the discussion here has been limited to a few examples of kinetic processes which have been studied using NMR spectroscopy. Closely related experimental techniques are electron paramagnetic resonance and Raman spectroscopies, which are discussed more fully by Strehlow [G4]. 

The known structures largely comprise the rod-like domain of the vimentin dimer, as illustrated in Fig. 3a. However, some segments have unknown structures. Experimental work using diffraction techniques has identified certain structural characteristics, and work based on Electron Paramagnetic Resonance measurements have revealed that the local stiffness of the LI and L2 domains (both helical structures) is close to that of the rod-like domain [65]. There appear to be persistent experimental challenges in identifying the remaining parts of vimentin IF structures. However, the intrinsic limitations in experimental methods call for the development of complementary computational methods that can provide a more controlled condition to assess the relation between the nanostructure and the nanomechanics of this class of materials. 

To obtain reliable experimental data and to correctly interpret them, we used such physicochemical and analytical techniques as dilatometiy, viscometiy, UV and IR spectroscopy, electronic paramagnetic resonance, light scattering spectroscopy, electron microscopy, and gas-liquid chromatography. To analyze the properties of polymeric dispersions, the turbidity spectrum method was used, and the efficiency of flocculants was estimated gravimetrically and by the sedimentation speed of special suspended imitators (e.g., copper oxide). 

Now, pulse Fourier spectroscopy is the preferred experimental technique in NQR. It was made possible by the introduction of inexpensive computers and by the development of FFT algorithms. Note that the principles of Fourier spectroscopy are well developed and widely used in other fields of spectroscopy, including magnetic resonance, electron paramagnetic resonance etc. Several monographs are available on this subject. The reader is referred to the... 

In investigations of the deformation and fracture of high polymer solids [4-67] by electron paramagnetic resonance techniques (EPR) similar experimental problems arise as during the above mentioned apphcations of EPR ... 

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