Nitrogen hyperfine interaction tensors

TABLE 10.4 Theoretical Values of the Eigenvalues of the Anisotropic Part of the Nitrogen Hyperfine Interaction Tensors"... 

The most significant are the Zeeman (g tensor) and nitrogen hyperfine interactions. These depend somewhat on chemical structure, solvent polarity, and temperature. An assumption has been made almost universally that magnetic parameters that are found in frozen solutions may be used to describe liquid phase spectra. This assumption should be recognized and considered carefully in precise work. It may be invalid for several reasons, including (1) altered distribution of nitroxide molecular conformations,... 

A detailed structural study has also been made of oxygenated cobalt(II) heme model systems and oxygenated Co(II) corrin complexes. " These used a combination of X-, Q- and W-band CW and pulsed EPR, X- and Q-band ENDOR, X-band HYSCORE and S-band ESEEM to determine the g and A tensors and investigate the proton and nitrogen hyperfine interactions. Both studies are excellent examples of the power of multi-frequency CW and pulsed ESR and ENDOR in determining the full electronic structure of metallo-complexes. 

Coordination causes electron-spin density redistribution in the N-O fragment the contribution of resonance structure II increase. The redistribution of spin density results in changes in the parallel component of the nitrogen hyperfine tensor. TEMPO and anthraquinone (AQ) have been used in this way to probe the Lewis acidity of alumina and Li and Mg doped alumina matrices.176 The differences in the Lewis acidic strength towards TEMPO and anthraquinone are discussed. An interesting study has appeared aimed to study the guest-host interaction between poly(amidoamine) dendrimers labelled with nitroxides and several porous solids including alumina.177... 

Intramolecular magnetic interactions in nitroxides are (1) the nitrogen hyperfine tensor (2) the g tensor (3) methyl proton hyperfine tensors (4) other proton hyperfine tensors (S) the nitrogen quadrupole coupling and (6) couplings to trace isotopes, mostly One desires to know how these properties depend on solvent and... 

Altaiskii et al [1] were the first to report on the ESR spectrum of nitrogen donors in Lely grown 3C single crystals. In that study the three-line spectrum is partially resolved. Later work by Carlos et al [2] showed that a well resolved three-line spectrum could be obtained for the CVD films as shown in FIGURE 1. The g-tensor and hyperfine interaction are isotropic with g = 2.0050 and A = 0.11 mT. Both of these parameters are in good agreement with expectations from simple effective-mass-approximation calculations for this polytype [5]. 

Unlike the isotropic hyperfine coupling constants, the anisotropic ones are mainly determined by dipole magnetic interactions. The contribution of the nearest atoms is expected to be suppressed by a distance factor. The values of AHC tensor are presented in Fig. 3. The results show that as in the previous case the tensor diagonal elements have the greatest values for the Ni atom varying from 70 to 150 MHz. But unlike to the previous situation the values for the nitrogen atoms are one order of magnitude lower as compared to the values for Ni atom. This is due to the fact that in this case the AHC constants are mainly... 

The interaction of nitric oxide (NO) with metal ions in zeolites has been one of the major subjects in catalysis and environmental science and the first topic was concerned with NO adsorbed on zeolites. NO is an odd-electron molecule with one unpaired electron and can be used here as a paramagnetic probe to characterize the catalytic activity. In the first topic focus was on a mono NO-Na" complex formed in a Na -LTA type zeolite. The experimental ESR spectrum was characterized by a large -tensor anisotropy. By means of multi-frequency ESR spectroscopies the g tensor components could be well resolved. The N and Na hyperfine tensor components were accurately evaluated by ENDOR spectroscopy. Based on these experimentally obtained ESR parameters the electronic and geometrical structures of the NO-Na complex were discussed. In addition to the mono NO-Na complex the triplet state (NO)2 bi-radical is formed in the zeolite and dominates the ESR spectrum at higher NO concentration. The structure of the bi-radicai was discussed based on the ESR parameters derived from the X- and Q-band spectra. Furthermore the dynamical ESR studies on nitrogen dioxides (NO2) on various zeolites were briefly presented. 

In nitroxide free radicals characterized by a hyperfine tensor. A, and g-tensor, g, the interaction between the magnetic moment of an unpaired electron and the magnetic moment of nitrogen nucleus is highly anisotropic. The anisotropy determines the line shape of electron spin resonance (ESR) spectrum of completely immobilized nitrox-ides (Fig. 1), and can be completely averaged out for fast thermal Brownian rotational diffusion in low-viscous media. For the " N nucleus with 7=1 and no other interacting nuclei in the nitroxide, three equidistant lines of equal intensities and widths should be observed in ESR spectra in such media. In fact, even in media of... 

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