Quadrupole effects

The quadrupole effects mentioned in Section I.B.(l) apparently are small, as magnetic susceptibility measurements18 have revealed that the energy differences between different orientations of an oxygen molecule in a /3-hydroquinone cavity become only noticeable at liquid helium temperatures. 

Quadrupole, effects, 25 moment, 188 resonance absorption, 190 Quasi-chemical theory, 122, 123, 128, 137... 

This expression is the same as that for the first-order quadrupole effect in high-field NMR spectra [4, 66]. The angular variation of (4.51) is visualized in Fig. 4.11. The graph on the left shows the contour of the function (3cos 0 1 ... 

D. Freude and J. Haase, 1993, Quadrupole Effects in Sdid-State Magnetic resonance, vol. 29. Springer-Verlag, Berlin. 

However, commonly due to a spread of quadrupole parameters caused by structural variation, with the extreme case being glassy or amorphous materials, the distinct features of fhe lineshape can be lost. This is particularly true if Cq is small. Then an approach which records spectra at several magnetic fields will allow bofh fhe second-order quadrupole effect parameter Pq, defined as... 

The same line shapes are observed in deuterium NMR of uniaxially elongated crosslinked rubbers118). On the basis of quadrupole effects (taking into account that... 

Static quadrupole effects in NMR are observed in solids (9) and also in anisotropic liquid crystals (10, 11, 12). For nuclei with spin quantum numbers, I, greater than V2, the distribution of positive charge over the nucleus can be nonspherical and the situation can be described in terms of a nuclear electric quadrupole moment. The interaction between the quadrupole moment, eQ and electric field gradients, eq, shifts the energy levels of the nuclear spin states. 

Chemical shift relative to liquid CS2, some are peak positions not the isotropic shifts, see original references. Numbers in parentheses represent singularity positions of MAS powder patterns, t Estimated upper limit of the quadrupole effect parameter, except which is based on lineshape analysis. 

The relative importance of these components is seen in Table 20, which contains a sampling of the calculated and observed data for 1,2-dichloroethane142. Many additional examples for this and other dihalides, as well as for haloketones and haloethers are available142,149. It is seen that benzene and xylene behave as solvents more polar than their dielectric constants would indicate this is observed in other cases, too. The quadrupole effect is clearly important and partly counteracts the dipole effect, while the polar effect is almost negligible. These principles have been incorporated into the molecular mechanics methodology, apparently with promising results150,151. 

Townes, C. H. and B. P. Dailey Nuclear Quadrupole Effects and Electronic Structure of Molecules in the Solid State. J. Chem. Phys. 20, 35 (1952). 

Investigations of the influence of lattice defects on NMR and the accompanying nuclear quadrupole effects have been studied in many papers (see references 125,161))... 

Blinc et al.4 in a classic paper on the NMR line shapes in PGs have presented the relation between the RF distribution and the quadrupole-perturbed NMR line shape for both first-order and second-order quadrupole effects. Static as well as time fluctuating RFs have been considered. By evaluating the local RF distribution, Blinc et al.4 have evaluated the Edwards-Anderson (qEA) order parameter. 

Magic angle spinning Si, Al and NMR spectra were recorded on a variety of spectrometers. The data reported here are from results obtained at 200 MHz proton. Thus, the Si, Al and frequencies are 39.7 MHz, 52.15 MHz and 81.0 MHz, respectively. Chemical shifts for aluminum are reported relative to A1(N03>3 in aqueous solution at infinite dilution and are not corrected for second-order quadrupole effects. The phosphorus and silicon chemical shifts are reported relative to 85 wt% H3P0 and Me Si, respectively. 

Cohen, M. H. and Reif, R (1957). Quadrupole effects in nuclear magnetic resonance studies of solids. In F. Seitz and D. Turnbull, eds. Solid State Physics. Academic Press, New York, p. 321. 

MQMAS was first proposed in 1995 by Harwood and Frydman [22, 23]. The aim of the technique is to refocus the second-order quadrupole effects, which otherwise... 

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