Spin echoes in half-integer quadrupole systems

The condition for an echo formation is reviewed in the context of half-integer quadrupole system. The common features of the classical echo phenomena and the coherence transfer echo are highlighted. The article also explains how the measurement of a series of coherence transfer echoes achieves the high-resolution feature of the multiple-quantum magic angle spinning (MQMAS) experiment. (C) 1999 John Wiley & Sons, Inc.