Quadrupolar and chemical shift tensors characterized by 2D multiple-quantum NMR spectroscopy

The present work discusses a new 2D NMR method for characterizing the princ ipal values and relative orientations of the electric field gradient and th e chemical shift tensors of half-integer quadrupolar sites. The technique e xploits the different contributions that quadrupolar and shielding interact ions impart on the evolution of multiple-quantum and of single-quantum cohe rences, in order to obtain 2D powder lineshapes that are highly sensitive t o these nuclear spin coupling parameters. Different spinning variants of th is experiment were assayed, but it was concluded that a static version can yield the highest sensitivity to the values of the principal components and to the relative geometries of the local coupling tensors. It was found tha t correlating the central transition evolution with the highest available o rder of the spin coherence was also helpful for maximizing this spectral in formation. Good agreement between data obtained on Rb-87 (S = 3/2) and Co-5 9 (S = 7/2) samples and ideal theoretical lineshape predictions of this exp eriment was obtained, provided that heterogeneities in the multiple-quantum excitation and conversion processes were suitably accounted by procedures similar to those described in the spin-1/2 multiple-quantum NMR literature. (C) 1999 Academic Press.