Spin-dipole

There are two terms of interest. First there is a classical electron spin-nuclear spin dipole-dipole interaction... 

We note that also other types of isovector giant resonances have been suggested as a source of information on the neutron skin, such as the spin-dipole giant resonance [33] and the isobaric analog state [34], At present studies of these reactions have not led to quantitative constraints for the neutron skin of... 

Gordy and Gordy and Morehouse derived an equation for calculating this average or effective distance based upon the assumption that the location of each spin dipole may be assigned approximately to a point. The result may be stated as in Eq. 1, in which 2D in gauss is the separation between the two outermost of the six (or four) lines, and R is the effective interelectronic distance in angstrom units ... 

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... 

Other Terms. Some small terms have not been included in Eq. (5) because it has never been necessary to include them to account for the observed ESR spectra. These include such terms as the nuclear spin-nuclear spin dipole interactions and the nuclear chemical-shift terms. These terms... 

Many metal ions have more than one unpaired electron similarly, certain organic species (diradicals and triplet and higher states) may have several unpaired spins. The effect of several electron spin dipoles in close proximity on... 

Fig. 3.18. Exponential recovery (A) of Mz(t) of a nuclear spin / dipole coupled to a paramagnetic metal ion. When I is also coupled to another nuclear spin J, the latter also coupled to the metal ion, non-exponentiality occurs. If J relaxes slower than /, curves B and C are obtained for a selective and a non-selective experiment respectively. If J relaxes slower than /, curves D (selective) and E (non-selective) are obtained. If J relaxes at the same rate as /, a selective experiment gives an intermediate behavior between curves B and D (not shown), while a non-selective experiment gives pure exponential recovery (A). It is apparent that in all cases non-selective experiments perform better than selective experiments, as they are less sensitive to the non-exponentiality introduced by I-J coupling. Conditions R m = 10 s l R M = 20 s l (B,C), 5 s l (D,E) and 10 s l (A). The I-J cross-relaxation rate ou (Chapter 7) is —20 s"1.

The magnetic spin dipole-dipole interaction is the most important source of nuclear spin relaxation for spin half (/ = ) nuclei. Apart from the relative orientations of the spins, the dipole-dipole interaction also depends on the length and orientation of the vector between the spins. Formally, it can be expressed as a tensor product of the 1st rank spin tensors, and and a 2nd rank... 

Furthermore, the lack of correlation of the different spins results in a decoupling of the different spin dipole-dipole interactions experience by the nuclear spin, Thus, even though there in general exists a correlation of the different dipole-dipole interaction tensors, the final expression for intermolecular relaxation time only consists of a sum of auto correlation functions of the individual interactions. 

An exception is the so-called triplet-type properties such as the Fermi-contact and spin-dipole contributions to indirect spin-spin coupling constants (for a discussion, see Ref. 44). 

The terms in equation (4) are generally referred to as the orbital-dipolar interaction (o) between the orbital magnetic fields of the electrons and the nuclear spin dipole, the spin-dipolar interaction (D) between the spin magnetic moments of the electrons and nucleus and the Fermi contact interaction (c) between the electron and nuclear spins, respectively. Discussion of the mathematical forms of each of these three terms appears elsewhere. (3-9)... 

C NMR spin-lattice relaxations in solid PMMAs of different tacticity were studied by CP/MAS NMR spectroscopy.324-328 The relaxation proceeds more slowly in isotactic PMMA than in syndiotactic PMMA even in the solid state this is because of the faster reorientation of the a-CH3 group in the isotactic chain.135 The nC-T times of the a-methyl carbons of PMMAs with different tacticities were measured over a wide range of temperatures by cross polarization, magic-angle spinning, dipole dephasing (CP/DD)... 

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