Multiple-quantum NMR with frequency-modulated chirp pulses

Frequency-modulated chirp pulses, for exciting multiple-quantum coherences over large bandwidths, can be considered as an alternative to composite pulses to combat the effects of large offsets and tilted effective fields. Refocusing of the phase dispersion of double-quantum coherence can be combined with suitable detection sequences to yield pure absorption 2-dimensional double-quantum spectra. The method of sym. excitation and detection by time-reversal may be applied to obtain t1-modulated longitudinal magnetization, which may then be converted into observable single-quantum coherence by a chirp echo sequence. Similar approaches can be used for many other NMR expts. involving coherence transfer. [on SciFinder (R)]