Chemical shift asymmetry parameter

Most valuable chemical information can be extracted from Mbssbauer parameters such as the isomer shift (5), the quadrupole splitting (AEq), the magnetic splitting (AEm), and the asymmetry parameter (n). 

Fig. 12 C -detected C CSA patterns of the SHPrP109 i22 fibril sample. The upper and lower traces correspond to the experimental and simulated spectra, respectively. Simulations correspond to the evolution of a one-spin system under the ROCSA sequence. The only variables are the chemical shift anisotropy and the asymmetry parameter. A Gaussian window function of 400 Hz was applied to the simulated spectmm before the Fourier transformation. (Figure and caption adapted from [164], Copyright (2007), with permission from Elsevier)...

Figure 1 Simulations of CT lineshapes corresponding to (A) static and (B) MAS experiments, for different values of the asymmetry parameter rjq.The positions of the isotropic chemical shift (c5iso) and some well-defined singularities are shown, in terms of the parameter A, defined in Equation 8. All simulations were done with the DMFIT software. ...

Fig. 4. Quadrupolar powder patterns (a) Spin NMR powder pattern showing that the central -)<- ) transition is broadened only by dipolar coupling, chemical shift anisotropy, and the second-order quadrupolar interactions, (b) Spin 1 NMR powder pattern for a nucleus in an axially symmetric electric field gradient (see text). The central doublet corresponds to 6 = 90° in Eq. (10). The other features of low intensity correspond to 6 = 0° and 6 = 180°. (c) Theoretical line shape of the ) - -) transition of a quadrupolar nuclear spin in a powder with fast magic-angle spinning for different values of the asymmetry parameter t (IS) ...

From the results shown in Table 1, the following conclusions can be drawn out Ci1 All the spectra correspond to non axially symmetric 31P tensors, (ii) the [dn - 033] difference ranges from 206 to 263 ppm and is definitely larger than the chemical shift difference observed in the liquid phase between a phosphonite and the corresponding thioxo-phosphonate, (iii) a linear relationship appears when the asymmetry parameter n is plotted against the intracyclic O-P-O bond angle a. 

The anisotropy AS, asymmetry parameter i] and isotropic chemical shift <5iso are expressed by the following equations ... 

Table 5.6. Oxygen-17 (both bridging, O, and nonbridging, 0 t) nuclear quadrupole coupling constants, asymmetry parameters (iq), and isotropic chemical shifts (8,) for the alkaline earth metasilicates"...

In C NMR spectroscopy, deviations from a Lorentzian lineshape, which is usually obtained in liquids, can be caused by a chemical shift anisotropy (CSA). If a CSA is present, the position of the resonance line depends on the relative orientation of the molecule with respect to the direction of the magnetic field applied (27,22). The superposition of the individual resonance lines results in typical lineshape patterns that can be described by two parameters the chemical shift anisotropy, AS, and the asymmetry parameter, Tj, respectively. In the case of an axially symmetric CSA tensor, i.e., 17 = 0, the relation between the resonance frequency, w, and the orientation of the molecule is given by... 

Fig. 3 The effect of slow magic-angle spinning. A set of spinning sidebands appears with a centre-band at the isotropic chemical shift and further lines spaced at the spinning frequency. The intensities of the sidebands change with spinning speed with higher-order sidebands (i.e., those further away from the centre-band) becoming less intense as the spinning speed increases. The chemical shift parameters used in the calculation of these sideband patterns are isotropic chemical shift offset 0 Hz chemical shift anisotropy 5 kHz asymmetry 0. Reproduced with permission from [16]...

Solid state 14N NMR measurements have been reported for ND4C1, (169) (CH3)4NMnCl (177) NH KSO. 12H20, (178) KCN, (179) NaCN (179) and Ba(N03)2. (180) These studies have yielded values for the 14N chemical shifts and quadrupole coupling constants and, where appropriate, the asymmetry parameter r in equation (35). By following the temperature dependence of the 14N relaxation time in the cubic phases of NaCN and KCN the activation energy of the reorientational motion of the cyanide ions is obtained. It is reported at 300 K to be 1-41 0-02 kcal mole-1 in NaCN and 0-50 0-25 kcal mole-1 in KCN. 079)... 

The traditional definitions of the three principal value components (5i 1, 22, and 533), isotropy 5iso, anisotropy and asymmetry of the chemical shift are equivalent to those of the magnetic shielding. This traditional scheme is indefinite. It leads to a loss of physical and chemical generality which is disadvantageous. Therefore, besides the isotropy two new parameters, span Q and skew k, are often introduced and used instead of the anisotropy A3 and... 

Solid-state NMR of the Rb has been employed to investigate the phase transitions in polycrystalline LiRbS04. The spin-lattice relaxation time Ti and the NMR line shape have been measured using MAS and MQ MAS methods between 373 and 488 K. The QCC, %, the asymmetry parameter, r, and the isotropic chemical shift, 5, have been determined from the analysis of MAS and MQ MAS spectra. The anomalies of x near the phase transition were associated with the deformation of the local environment of the Rb ions in the crystal lattice. 

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