Far-off-resonance averaging of dipolar interactions in solids

The far-off-resonance performance of several line-narrowing sequences is investigated. Both theoretically and experimentally, it is found that transverse relaxation times, dominated by dipole-dipole interactions, are most effectively prolonged not only on-resonance but also for certain, generally large, resonance offsets. These correspond to a situation when, during the basic pulse separation, the frequency offset rotates the toggling-frame Hamiltonian by multiples of 180 degrees. The implications of these results for the study of macroscopic translational diffusion using static-held-gradient NMR are discussed. (C) 1997 Academic Press.