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]. 

Isotope Spin Natural abundance (A) (%) vo at 9.4 T Relative receptivity" Quadrupole moment (fm2)7 Quadrupole broadening factor4 Stemheimer antishielding factor (70c) ... 

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

Nucleus I Natural abundance (%) Vo (MHz) at 7.05 T Relative receptivity Quadrupole moment (mb) Quadrupole broadening factor Stemheimer antishielding factor (y)... 

La is a spin I = /2 nucleus with a 99.9% natural abundance and good NMR sensitivity, but its utility for solid-state NMR studies is limited by its quadrupole broadening which is greater by a factor of about 30 than for Al in sites with the same structural distortion and in the same magnetic field. The chemical shifts of La are normally quoted with respect to aqueous LaCla solution. 

Various ID and 2D experiments related to first-order quadrupole broadening also benefit from the fast rotation frequency. For heavier nuclei, quadrupole interaction and chemical shift anisotropy averaging at higher speeds results in better focusing of signal intensity to the remaining rotation sidebands (Fig. 5). 

For all the oxides calcined at Tc<973 K, octahedral (Al, 2-10 ppm), pentahedral (Al, 23-35 ppm) and tetrahedral (Al, 54-65 ppm) aluminum were detected, the latter being most abundant (Fig. 1 to 4, Tables 2 and 3). All the signals were not well resolved and relatively wide due to quadrupole broadening. Thus, a exact quantification of the different aluminum species by deconvolution-integration was rather difficult. Nevertheless, the method could provide a good estimate of the amounts of Al in different coordinations [6]. No effect of the synthesis additive was found on the A1 speciation in alumina... 

The l = 2 terms in the multi-pole expansion (8.32), which are linear in the electric field gradient (<9E/dz)r=0, are known as the quadrupole terms [89,90] and they produce a broadening of the shallow impurity lines known as the quadrupole broadening. At a difference with the quadratic Stark broadening, the quadrupole broadening results in a more symmetric profile of the perturbed line [90]. 

Solid solutions of iron in /5-Mn are paramagnetic at room temperature. Iron substitutes at both types of site in the structure, and shows no more than a slight quadrupole broadening [40]. Additional broadening at 4-2 K for... 

Moderate quadrupole moment for nitrogen. This intermediate case leads to peak broadening, called quadrupole broadening, rather than splitting. The attached proton (as in N—H) is not sure of what it sees. ... 

Figure 6.12, the NMR spectrum of pyrrole, shows an extreme example of quadrupole broadening, where the NH absorption extends from 7.5 to 8.5 ppm. 

Quadrupole broadening usually affects only the proton (or protons) attached directly to nitrogen. In the proton NMR spectrum of an amide, we expect to see the NH proton appear as a very broad singlet. In some instances, however, one might observe the protons on a carbon atom next to the nitrogen split... 

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] ... 

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