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 th at transverse relaxation times, dominated by dipole-dipole interaction s, are most effectively prolonged not only on-resonance but also for c ertain, generally large, resonance offsets. These correspond to a situ ation when, during the basic pulse separation, the frequency offset ro tates the toggling-frame Hamiltonian by multiples of 180 degrees. The implications of these results for the study of macroscopic translation al diffusion using static-held-gradient NMR are discussed. (C) 1997 Ac ademic Press.