SPIN-ECHO MODULATION EXPERIMENTS WITH SOFT GAUSSIAN PULSES

An analysis is presented for a homonuclear spin-echo experiment in whi ch refocusing and spin inversion are implemented by simultaneous soft 180 degrees pulses applied to two weakly coupled spins, It is shown th at for this experiment, simple pulses of short duration (for example, Gaussian pulses) are preferable to more complex shapes such as BURP pu lses or Gaussian cascades, since this limits the generation of undesir able multiple-quantum coherence. An expression is derived for the opti mum delay between excitation and detection for the generation of anti- phase magnetization at the two sites. The theoretical results are in g ood agreement with experiment. The doubly selective spin-echo techniqu e is shown to be useful for the determination of small unresolved spin -spin splittings, and this is illustrated with results from the 400 MH z proton spectrum of strychnine. (C) 1996 Academic Press, Inc.