Theoretical formalism and experimental confirmation of intermolecular dipolar effects under time-averaged magnetic field gradients
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A general analytical expression for intermolecular dipolar effects in liquids under the influence of magnetic field gradients of varying magnitudes, directions, and durations was explicitly derived with the density matrix formalism. We demonstrate that the time-averaged, not instantaneous, orientation of the applied gradients determines the contributions of long-range intermolecular dipole effects to multiple-quantum coherences. Theoretical and experimental results demonstrate, for the first time, that when the time-averaged orientation of a series of gradient pulses during the evolution period is at the magic angle, intermolecular dipolar effects are suppressed. The experimental evidence presented herein strongly supports our theoretical predictions. (C) 1999 Elsevier Science B.V. All rights reserved.