Quadrupolar-driven recoupling of homonuclear dipolar interactions in the nuclear magnetic resonance of rotating solids

We discuss the recoupling of homonuclear dipolar interactions between quadrupolar nuclei under magic-angle spinning conditions, caused by the first-order quadrupolar interaction. This recoupling leads to NMR linewidths displaying a nonmonotonic dependence on the spinning frequency, meaning that broader lines may result as the spinning rate is increased. The effect depends on geometrical parameters of the spin system, which makes it suitable for distance measurements and for obtaining the relative orientations of dipolar and quadrupolar tensors. We propose a theoretical model of the dipolar recoupling based on average Hamiltonian theory, and find it in good agreement with numerically exact simulations and experiments on I=3/2 systems. (C) 2001 American Institute of Physics.