Second-order quadrupole broadening

The ZB and WZ forms of ZnS could be distinguished on the basis of their isotropic 67Zn and 33S static NMR chemical shifts [63] however, estimates of small CSAs obtained from static 33S NMR of the WZ forms of ZnS and CdS were obtained by ignoring any small second-order quadrupole broadening [65], which may account for discrepancies when NQCCs are assumed to be responsible for the broadenings [65]. 

A characteristic broadening of the central transition can be observed in the case of strong quadrupole interaction (second-order quadrupole broadening). The second moment, Mf of the central transition with respect to its center of gravity is given by [12] ... 

The complete suppression of the influence of second-order quadrupole broadening requires the application of double rotation (DOR) [34-36] or dynamic angle spinning (DAS) [37-39] techniques. 

Quadrupole broadening factor the second-order quadrupolar broadening of the central transition which is proportional to... 

A further factor to be taken into account when assessing the relative ease with which a quadrupolar nucleus may be observed is the width of the line which is determined for a given electric field gradient by the quadrupole moment (also listed in Table 1.2). Often only the central transition is observed, for which the linewidth is determined by its second-order quadrupolar broadening and is proportional to [Q (I(I +... 

Figure 2.9. The quadrupole perturbed powder patterns for an I = nucleus. A. The outer satellite transitions to first-order. B. The second-order quadrupolar broadening of the central transition with...

The resonance frequencies of the isotopes Mo and Mo are very similar, differing by only 2%, but the sensitivity of Mo and its significantly smaller second-order quadrupolar broadening make it the preferred Mo NMR nucleus even though Mo has the advantage of relaxing much faster in cases where quadrupole relaxation is dominant. 

With the advent of higher-field spectrometers that substantially reduce line-broadening due to the second-order quadrupole effect [30] and with the use of multiple-quantum techniques for eliminating such line-broadening effects [31], one can expect that NMR techniques will play an increasingly important role in the study of silica and modified silica systems. Of course, the very low natural abundance of this nuclide remains a substantial constraint on such applications. 

Quadrupole Effect. The spin of lh is I = 5/2. The cubic symmetry of the latHfiPImplies that thft filftctric field gradient at the In nuclei vanishes if the lattice is undistorted. However, lattice defects in impurities disturb the symmetry and give rise to line broadening. The center of the line is shifted because of the second-order quadrupole effect ... 

NMR spectra, where the v. axis nearly purely reflects the isotropic chemical shift, and the quadrupolar parameters (second-order quadrupolar broadening and quadrupole-induced shift) are separated along the V axis (Fig. 19D). 

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