Multiple-pulse n.m.r. experiments in solids: an introduction to symmetrized pulse sequences

The study of solids by n.m.r. has been greatly facilitated with the development, over the last 10 years or so, of sophisticated r.f. multiple-pulse experiments designed to reduce the dipolar interaction. Often when the intrinsic dipolar line broadening is selectively reduced in many materials, smaller and usually more interesting chemical shift and exchange interactions are revealed that reflect the solid state electronic structure around the resonant nuclei. This situation obtains in liquids, of course; however, in solids the full interaction tensor components are measurable and yield valuable additional information on the chemical bonding. In this paper the development of the various multiple pulse techniques is reviewed and their detailed operation described in a consistent formalism.