Simultaneous soft pulses applied at nearby frequencies

The rotation of a spin subject to an on-resonance soft pulse and simultaneo usly to a soft pulse at a nearby frequency may strongly deviate from the de sired rotation expected for a single on-resonance pulse. The deviation is t he result of transient frequency shifts of the spin caused by the off-reson ance irradiation. We show that the resulting error can be corrected by shif ting the frequency of the on-resonance pulse in such a way that it tracks t he shift of the spin frequency. Experimentally, the effectiveness of this s imple and intuitive method is demonstrated for simultaneous inversions at n earby frequencies in the case of both coupled and uncoupled spins, Simulati ons predict that the correction technique is effective for arbitrary pulse shapes and tip angles and is particularly useful when the frequency window of the shaped pulse is two to eight times the frequency separation between the chemical shifts of the two spins, (C) 2000 Academic Press.