Determination of absolute quadrupolar tensor orientations by double-quantum NMR on powders

We introduce a new nuclear magnetic resonance (NMR) approach for determining electric field gradient (‘quadrupolar’) tensor orientations directly from polycrystalline powders. It involves a homonuclear 2D experiment that correlates (two-spin) double-quantum and single-quantum coherences of half-integer quadrupolar spin nuclei undergoing magic-angle-spinning. The 2D NMR spectrum is sensitive both to the relative orientations between the correlated quadrupolar tensors and to their orientations relative to the dipolar vector of the spin-pair. A novel strategy to calculate 2D spectra from multi-spin systems is used to extract the tensor orientations. We demonstrate the method by estimating the three 23Na quadrupolar tensor orientations in Na 2 SO 3 .