Quadrupole effects in the magic-angle-spinning spectra of spin-1/2 nuclei

Abstract

Magic-angle spinning fails to eliminate the effect of dipolar coupling on the spectrum of a spin-1/2 nucleus (e.g., 13C ) coupled to a quadrupolar nucleus (e.g., 14N). A quantitative theory of this phenomenon, based on an adiabatic approximation, is presented, together with numerical simulations of spectra. The spectrum is sensitive to the sign and magnitude of the electric-field gradient at the quadrupolar nucleus, the angles between principal axes of the dipolar and quadrupolar interaction tensors, and the orientation of the spinning axis with respect to the external magnetic field.