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

We discuss the recoupling of homonuclear dipolar interactions between quadr upolar nuclei under magic-angle spinning conditions, caused by the first-or der quadrupolar interaction. This recoupling leads to NMR linewidths displa ying a nonmonotonic dependence on the spinning frequency, meaning that broa der lines may result as the spinning rate is increased. The effect depends on geometrical parameters of the spin system, which makes it suitable for d istance measurements and for obtaining the relative orientations of dipolar and quadrupolar tensors. We propose a theoretical model of the dipolar rec oupling based on average Hamiltonian theory, and find it in good agreement with numerically exact simulations and experiments on I=3/2 systems. (C) 20 01 American Institute of Physics.