Investigation of variable angle sample spinning (VASS) NMR of quadrupolar nuclei. I. Theory

Abstract

Variable angle sample spinning NMR of quadrupolar nuclei in the solid state has been theoretically investigated in order to determine the optimal angles to achieve high-resolved and quantitative spectra. The earlier literature contributions have been included in a more general model. Complete analytical expressions were derived and are reported for all possible cases. It is concluded that magic angle spinning (at 54.7°) is to be used whenever the dipolar interactions and/or the chemical shift anisotropy dominate the spectra. For the other cases, θ=43.5° (which would allow an easy discrimination of the quadrupolar frequency and the asymmetry parameter), and θ=60°–70° (where the linewidth is half of that obtained for MAS conditions) are proposed as preferred spinning angles.