Magnetic moment, isotropic

While the combination of the heteronuclear dipolar decoupling and MAS provides a mean to obtain high-resolution isotropic spectra in solids, the serious problem still remains in addition to the relatively small magnetic moment and low natural... 

Before formally developing the tensor it is perhaps worthwhile to discuss the various types of interactions which contribute to it. The coupling between nuclear and electron magnetic moments are conveniently divided into those which are isotropic and those which depend on orientation. The former is the result of the impaired electron having a finite probability of being at the nucleus. This type of interaction is termed the contact interaction, and is described by the constant,... 

In transition metal complexes there may be a substantial orbital magnetic moment (reflected by deviations of the g-values from ge) which leads to an isotropic as well as an anisotropic contribution to the hf interaction125,132. These contributions arise from a second order term of the form % Vtu 9 Lsl l/ o), where fm denotes the MO of... 

Figure 6. Li MAS NMR spectrum of the layered compound Li2MnOs acquired at a MAS frequency, Vr, of 35 kHz. Spinning sidebands are marked with asterisks. The local environment in the Mn +/Li+ layers that gives rise to the isotropic resonance at 1500 ppm is shown. Spin density may be transferred to the 2s orbital of Li via the interaction with (b) a half-filled t2g orbital and (c) an empty d/ Mn orbital to produce the hyperfine shifts seen in the spectrum of Li2MnOs. The large arrows represent the magnetic moments of the electrons in the t2g and p orbitals, while the smaller arrows indicate the sign of the spin density that is transferred to the Li 2s and transition-metal d orbitals.

The six high spin Fe sites in the [(Fe6S5X5)(M(CO)3)2]" anions are antiferromagnetically coupled as evidenced by the reduced ambient temperature magnetic moments, and the temperature dependence of the isotropically shifted resonances in the aryloxide derivatives. 

In addition to the isomer shift and the quadrupole splitting, it is possible to obtain the hyperfine coupling tensor from a Mossbauer experiment if a magnetic field is applied. This additional parameter describes the interactions between impaired electrons and the nuclear magnetic moment. Three terms contribute to the hyperfine coupling (i) the isotropic Fermi contact, (ii) the spin—dipole... 

There is also an intuitive mode to see the effect of an isotropic electron magnetic moment on a nucleus. Fig. 2.7 illustrates that, indeed, the dipolar magnetic field experienced by the nucleus for different orientations of the metal-nucleus vector with the magnetic field changes sign, being positive when the... 

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