Coupling constants, quadrupole

Dechter J J, Henriksson U, Kowalewski J and Nilsson A-C 1982 Metal nucleus quadrupole coupling constants in aluminum, gallium and indium acetylacetonates J. Magn. Reson. 48 503-11... 

Nuclear electric quadrupole QCC (quadrupole coupling constant), (asymmetry parameter) Line-shape analysis, nutation NMR Coordination symmetry... 

T. P. Das and E. L. Hahn, Nuclear Quadrupole Resonance Spectroscopy, Academic Press, New York, 1958, 223 pp E. A. C. Lucken, Nuclear Quadrupole Coupling Constants, Academic Press, London, 1969, 360 pp. 

The interaction energy depends on Gn, and v and the allowed energy levels turn out to depend on eQ q. Division by h gives eqQ jh which we refer to as the quadrupole coupling constant (QCC). 

Quadrupole coupling constants for molecules are usually determined from the hyperfine structure of pure rotational spectra or from electric-beam and magnetic-beam resonance spectroscopies. Nuclear magnetic resonance, electron spin resonance and Mossbauer spectroscopies are also routes to the property. There is a large amount of experimental data for and halogen-substituted molecules. Less data is available for deuterium because the nuclear quadrupole is small. 

The author concerns himself with a comparison between theoretical and experimental studies of simple molecules containing the C = N linkage. A large number of spectroscopic studies have been made for XCN molecules, and in the majority of cases many isotopic species have been studied. The experimental data is very accurate. An interesting feature of such molecules is that the C s N distances are equal to within experimental error, and one might expect that the quadrupole coupling constants would be similar. This is not the case, as shown in Table 16.4. 

Sb Mossbauer spectra of SbSBr, SbSI, SbSeBr, SbSel, and SbTel have been obtained at 4.2 K. The quadrupole coupling-constant of the iodides decreases in the order SbSI > SbSel > SbTel, becoming nega-... 

Schwerdtfeger, P., Pernpointner, M. and Nazarewicz, W. (2004) Calculation of Nuclear Quadrupole Coupling Constants, in Calculation ofNMR and EPR Parameters Theory and Applications, (eds M. Kaupp M. Biihl and V.G. Malkin), Wiley-VCH Verlag GmbH, Weinheim, pp. 279-291. 

The experimentally observed quadrupole splitting AEq for Fe in inorganic compounds, metals, and solids reaches from 0 to more than 6 mm s [30, 32]. The range of AEq for other Mossbauer isotopes may be completely different because of the different nuclear quadrupole moment Q of the respective Mossbauer nucleus, and also because the EFG values may be intrinsically different due to markedly different radial distributions of the atomic orbitals (vide infra). As Q is constant for a given isotope, variations in the quadrupole coupling constants eQV can only arise from... 

Chemical information from hafnium Mossbauer spectroscopy can primarily be deduced from the quadrupole-splitting parameter. In Table 7.4, we have listed the quadrupole coupling constants eQV for some hafnium compounds. Schafer et al. 

Table 7.4 Quadrupole coupling constant eQV z and asymmetry parameter r) for hafnium compounds...

W(VI) compounds with 5cP electronic configuration, the EFG is reasonably weU described by the lattice contribution only. The regular octahedral WOs structure yields zero EFG in agreement with experiment, while the deformed tetrahedral W04 strucmre results in significant quadrupole coupling constants of either sign, e Q > 0 and also <0, depending on the distortion of the O4 tetrahedron. 

Table 7.7 Quadrupole coupling constants e qQ (mm 7 = Kti — VyyiVzz, and experimental line width tungsten compounds...

Table 10 BH HLYP/aug-cc-pVTZ calculated nuclear quadrupole coupling constants /(N) and /(Hal) [MHz] of the complexes XY- -NH3 a ...

Other key properties of these complexes relevant for comparison with experiment are the nuclear quadrupole coupling constants. Theoretical NQCC values, as calculated via electric field gradients, are discussed exhaustively in several recent theoretical investigations [26,28,30,33,34] and in experimental work [4-11]. BH HLYP/aug-cc-pVTZ calculated NQCCs [30,34], as evaluated for XY- -NH3 complexes, are listed in Table 10. 

In Sect. 2, it was indicated that changes AXap(X) and A/ / (Y) in halogen nuclear quadrupole coupling constants xap X) and Xafs(Y) of a dihalogen... 

We assume that, on formation of B- XY, a fraction 5j (i = intermolecular) of an electronic charge is transferred from the electron donor atom of Z of the Lewis base B to the npz orbital of X and that similarly a fraction 5p (p = polarisation) of an electronic charge is transferred from npz of X to n pz of Y, where z is the XY internuclear axis and n and n are the valence-shell principal quantum numbers of X and Y. Within the approximations of the Townes-Dailey model [187], the nuclear quadrupole coupling constants at X and Y in the hypothetical equilibrium state of B- -XY can be shown [178] to be given by ... 

Fig. 20 Variation of the fraction <5 of an electronic charge transferred from B to XY on formation of B- XY with the ionisation energy 7b of B for the series XY = 02, BrO and IO. See text for the method of determination of Si from observed XY nuclear quadrupole coupling constants. The solid curves are the functions <5 = A exp(- al ) that best fit the points for each series B- XY. Data for B- -B are nearly coincident with those of B- BrO and have been excluded for the sake of clarity...

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