Dynamic-angle spinning of quadrupolar nuclei

In dynamic-angle spinning (DAS), a sample spins around an axis inclined at an angle [Formula presented] with respect to the magnetic field such that the averages of [Formula presented] are zero. The simplest case is where [Formula presented] assumes two discrete values [Formula presented] and [Formula presented] (complementary DAS angles) such that the averages of [Formula presented] and [Formula presented] are zero, thereby removing second-order quadrupolar (and dipolar) broadening. Examples of DAS complementary angles are [Formula presented] and [Formula presented]. Experimental details for DAS experiments are provided and applications to sodium-23 and oxygen-17 NMR illustrate the enhanced resolution achieved by removing the second-order broadening inherent in magic-angle spinning.