Electric quadrupolar interaction

In the presence of a small simultaneous electric quadrupolar interaction, the split levels are shifted by an amount s, which is called the quadrupole shift parameter and is given by the following ... 

Serious complications arise, however, if the spins are subject to strong nuclear electric quadrupolar interactions, which tend to modify the echo amplitudes measured. In such cases, it is still possible to extract dipole-dipole coupling information from spin echo decay spectroscopy, if the 71-pulses are applied entirely selectively to the central l/2>o -l/2> transition [6]. If the resonance frequencies between the coupled nuclei are sufficiently similar to allow for spin-exchange via the flip-flop mechanism, Eq. (5) turns into... 

Finally, a few words remain to be said about case (d) (S>l/2,I>l/2). At the present stage of knowledge, this case remains seemingly intractable for quantitative applications outside the non-selective excitation limit Vj/Vq l. The chief problem in applying pulse sequence at Fig. 8b) arises from the nuclear electric quadrupolar interactions affecting the S spins, which interfere with the ability of the 71-pulse trains to refocus the transverse magnetization. In contrast, pulse sequence at Fig. 8a) is able to produce experimental REDOR curves, which are, however, difficult to interpret quantitatively. As a best-effort solution, one may resort to sample-to-sample comparisons on a relative basis and the use of empirical calibration procedures with closely related model compounds [32]. Alternatively, the SEDOR approach, which does not suffer from these restrictions, would be preferable. 

Because NMR deals with radio frequencies where the spontaneous radiation is rather weak, the interaction Hamiltonians can be written in semiciassical form, i.e., the r.f. field can be described by classical quantities such as magnetic field, B. In solid-state NMR, the most important interactions are diemical shift, dipolar, and electric quadrupolar interactions. Dipolar interactions can also be divided into direct... 

The magnetically induced electric quadrupolar interaction was recently observed in several cubic, ferromagnetically ordered intermetallic compounds at the nucleus of the rare-earth S-state ions Gd and Eu, despite the fact that the nuclei are residing on nominally cubic lattice sites e.g., nuclear quadrupole... 

For Zn SSNMR spectroscopy, the observed spectrum is usually dominated by the nuclear electric quadrupolar interaction unless the zinc sits at a site with spherical symmetry (such as tetrahedral, octahedral and cubic sites). This anisotropic interaction originates from the coupfing between the quadrupole moment (eQ) of the nucleus and the electric field gradient (EFG) at the nuclear site. The EFG is described by a second-rank tensor that can be diagonalized in a principal axis system (PAS). In the PAS, the EFG is described by three components, which are ordered in such that I Fxx I kVy I ud they satisfy FxxT TyyT Tzz fi-The quadrupolar interaction is characterized by two parameters one is quadrupolar coupling constant ... 

Another form of spin-lattice relaxation occurs when there is a quadrupolar nucleus vide infra) present in the paramagnetic species. Associated with this nucleus is an electric quadrupolar field, which will interact with gradients in the electric component of the microwave radiation. However, as this electric quadrupolar interaction is generally weak, it does not contribute much towards the relaxation. 

The second turn of the discussion around the nature of a SHG in nematic liquid crystals arised when the SHG was observed in oriented layers of 4-methoxybenzylidene-4 -butylaniline (MBBA)/ The phenomenon has been explained by the lack of the symmetry center in the nematic phase. The zero-field SHG in MBBA was also investigated but the nature of the effect was connected with the flexoelectric polarization of surface layers. Such a polarization has to remove the inversion center in surface liquid crystalline layers and to allow the SHG to be detectable. Another explanation of the zero-field SHG in terms of the electric quadrupolar interaction was suggested in. ... 

The dipole-dipole interaction involves multiple spins. Therefore, it may be complicated to handle in comparison with chemical shift and electric quadrupolar interactions. However, it is simple to examine two interacting proton spins in the high-field approximation as... 

Less important contributions are the magnetic dipolar and electric quadrupolar interactions. The Anderson type of superexchange (virtual transfer of a 4f electron via p states of the anion from one site to another) has to be ruled out for insulators (Eu chalcogenides), since it is an order of magnitude too small to explain the observed ordering temperatures (Kasuya 1970), and p-d mixing has to be considered. 

Figure 4.45 Three main types of hyperfine interactions a monopolar interaction, b electric quadrupolar interaction and c magnetic dipolar interaction. Adapted from [138]...

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