Composite puise excitation in quadrupole echo spectroscopy

An examination of several composite pulse quadrupole echo sequences designed for the broadband excitation of I=1 systems shows that these sequences reduce but do not eliminate finite pulse width effects. It is demonstrated both experimentally and theoretically that these sequences can also introduce additional distortions. The origin of these distortions and several aspects of the evaluation of broadband excitation sequences are discussed. It is shown that these distortions can be eliminated by employing higher order composite pulses. Finally the viability of composite pulse excitation for systems undergoing chemical exchange is discussed.