The nonlinear stimulated echo in the presence of inequivalent spins

A sequence of three RF pulses in the presence of magnetic field gradients at high magnetic fields (greater than or similar to 7 T) produces multiple nonlinear stimulated echoes (NOSE) at times nrl after the third pulse, where n is an integer and tau(1) the interval between the first two pulses. From the classical point of view, these phenomena are due to the demagnetizing field produced by the spatial modulation of the nuclear magnetization arising in the sample after the first two pulses, In this paper the behavior of NOSE for molecules containing inequivalent uncoupled spins subject to motional averaging of short-range interactions is reported. As a consequence of the demagnetizing field the interference between the magnetizations of the different spin ensembles leads to beats in the amplitude of NOSE. A semiclassical formalism describing this dependence is established and verified in test experiments with the protons in a methyl acetate sample. (C) 1998 Academic Press.