THE DIPOLAR-SPLITTING-RATIO METHOD - A CONVENIENT APPROACH TO THE ANALYSIS OF DIPOLAR-CHEMICAL-SHIFT NMR-SPECTRA OF STATIC POWDER SAMPLES

The NMR lineshape of an isolated pair of spin- 1 2 nuclei in a static powder sample depends on the three principal components of the chemical-shift (CS) tensor, the direct dipolar spin-spin coupling tensor, and their relative orientations. Provided that the CS anisotropy is much greater than the effective dipolar coupling constant, Reff, splittings appear at frequencies near those corresponding to each of the principal components of the CS tensor. The magnitude of the splittings provides important information concerning the orientation of the principal components of the CS tensor. Unfortunately, the equations that are generally solved to obtain this information are not independent. As a result, the values obtained for the two angles which describe the orientation of the CS tensor may not be unique. Here, we present a convenient approach, the dipolar-splitting-ratio method, which immediately indicates all possible solutions. Examples are presented to demonstrate the utility of our method in obtaining orientation information from powder samples. © 1994 Academic Press. All rights reserved.