ORIGIN OF THE CORRELATION TIME-DEPENDENCE OF COHERENCE TRANSFER DISTORTIONS IN ROTATING-FRAME CROSS-RELAXATION SPECTRA

HOHAHA distortions in conventional (CW) ROESY experiments are known to be prominent when the frequency of the spin-lock field is near the mi dpoint between the resonance frequencies of a pair of coupled spins. T hat the disappearance of these distortions with offset from the midpoi nt is more rapid for large molecules than smaller ones is less widely known, and less well understood. We provide a quantitative explanation of the latter phenomenon using a combination of theory and numerical simulations. The cause of this effect can be found in the differential relaxation of the various magnetization modes which are involved in H OHAHA transfer. These modes experience enhanced relaxation far from a Hartmann-Hahn match. This enhancement is larger for molecules Which ha ve long correlation times. (C) 1997 Academic Press.