ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
A procedure for determining the interaction tensor orientations and the interaction parameters for mutually oriented electric field gradient (efg) or dipolar and shielding tensors has been developed based upon the magnetic field dependence of the critical frequencies from the polycrystalline nuclear magnetic response (NMR) spectrum. The central transition line shape of half-integer quadrupolar nuclei in the presence of mutually oriented shift anisotropy and second order quadrupolar interaction is discussed for the first time. Analytical expressions for the field dependent critical frequencies have been determined for special orientations when the shift principal Z axis lies on the XZ, YZ, or XY plane of the efg (or dipolar) tensor for the first order as well as the second order interactions. The plots resulting from the analytical expressions provide a convenient graphical approach in determining approximate tensorial orientations and interaction parameters through pattern recognition. For general orientations, a numerical procedure has been developed to determine these parameters by iteratively minimizing the squares of the differences of the calculated and the experimental critical frequencies. Higher order perturbation terms can be incorporated in the present treatment. The method is demonstrated by variable field static proton spectra of trichloro–acetic acid at three different fields (1.3, 2.3, 5.2 T). The near-orthogonal orientation between the dipolar and shielding tensors and the interaction parameters obtained from this approach are consistent with those obtained previously from single crystal studies.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.457069
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