Magnetic field gradients in solid state magic angle spinning NMR

Magnetic field gradients have proven useful in NMR for coherence pathway se lection, diffusion studies, and imaging. Recently they have been combined w ith magic angle spinning to permit high-resolution measurements of semi-sol ids, where magic angle spinning averages any residual dipolar couplings and local variations in the bulk magnetic susceptibility. Here we show the fir st examples of coherence pathway selection by gradients in dipolar coupled solids. When the gradient evolution competes with dipolar evolution the exp eriment design must take into account both the strength of the dipolar coup lings and the means to refocus it. Examples of both homonuclear and heteron uclear experiments are shown in which gradients have been used to eliminate the need for phase cycling. (C) 1999 Academic Press.