Dynamic-angle spinning of quadrupolar nuclei. 1990

In dynamic-angle spinning (DAS), a sample spins around an axis inclined at an angle θ(t) with respect to the magnetic field such that the averages of P_n(cosθ) are zero. The simplest case is where θ(t) assumes two discrete values θ₁ and θ₂ (complementary DAS angles) such that the averages of P₂(cosθ) and P₄(cosθ) are zero, thereby removing second-order quadrupolar (and dipolar) broadening. Examples of DAS complementary angles are θ₁=37.38° and θ₂=79.18°. 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.