Metals anisotropic constants

As mentioned above, in an ENDOR experiment the rf field is swept while the static magnetic field is held at a constant position in the EPR spectrum. For slow sweep rates and narrow EPR lines a device would be desirable which is able to stabilize the ratio of the microwave frequency to the static magnetic field. The applicaiton of a commercially available field/frequency lock system is restricted to a region of 6 mT about the DPPH resonance field33). In metal complexes with strongly anisotropic EPR spectra, however,... 

Once a description of the electronic structure has been obtained in these terms, it is possible to proceed with the evaluation of spectroscopic properties. Specifically, the hyperfine coupling constants for oligonuclear systems can be calculated through spin projection of site-specific expectation values. A full derivation of the method has been reported recently (105) and a general outline will only be presented here. For the calculation of the hyperfine coupling constants, the total system of IV transition metal centers is viewed as composed of IV subsystems, each of which is assumed to have definite properties. Here the isotropic hyperfine is considered, but similar considerations apply for the anisotropic hyperfine coupling constants. For the nucleus in subsystem A, it can be... 

Randomly distributed dipolar molecules form an isotropic medium characterized by a single refractive index n. When these molecules are more or less aligned in an electric field the medium becomes anisotropic and its optical properties must be described by two refractive indices. The Kerr cell consists of a glass vessel fitted with two parallel optical windows and two metal electrodes (Figure 2.11). The cell contains a liquid or a gas (solids can also be used) when an electric field exists between the electrodes the phase difference between the electric vectors is proportional to the square of the field and to the value of the electrical Kerr constant of the dielectric... 

The range of application of the integral equation method is not limited to the standard dielectric model. It encompasses the cases of anisotropic dielectrics [8] (liquid crystals), weak ionic solutions [8], metallic surfaces (see ref. [28] and references cited therein),. .. However, it is required that the electrostatic equation outside the cavity is linear, with constant coefficients. For instance, liquid crystals and weak ionic solutions can be modelled by the electrostatic equations... 

The isotropic and anisotropic hyperfine coupling terms in a arise from interactions between electron and nuclear spins, and provide information about the nature of the orbital containing the unpaired electron and the extent to which it overlaps with orbitals on adjacent atoms. The anisotropic term can cause similar difficulties to the g tensor anisotropy in analysing spectra of polycrystalline powders extracting coupling constants from spectra of transition metal ions or radicals in zeolites can be difficult or impossible without computer simulation. 

Transition Metal Complexes Attempts have been made to use the Fermi contact portion of the metal ion s hyperfine interaction to determine electron distribution in transition metal complexes, but these attempts have not been very successful or useful. Most of the useful data have been obtained from the anisotropic portion of the hyperfine constant as determined from single-crystal or supercooled solution studies. For ligand nuclei both the isotropic and anisotropic parts of the hyperfine interaction have yielded useful results on electron distribution. Although the most useful data still come from the anisotropic portion of the hyperfine interaction, there is need for more work in this area in that the available data are rather sparse for many important types of complexes. 

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