Effect of remote cross correlations on transverse relaxation

The effect of remote cross correlations on the transverse-relaxation rates of single- and multiple-quantum coherences in isotropically reorienting molecules is investigated for homonuclear AX, AMX, and AMKX spin systems, It is found that the remote cross correlations have a first-order contribution to the single- and multiple-quantum linewidths which is purely a differential effect and is observable only in the presence of resolved J couplings. In the absence of J couplings, the first-order contribution cancels and the remote cross correlations give rise to a second-order effect which becomes observable only in the presence of direct cross correlations. In the absence of J couplings and direct cross correlations, the remote cross correlations drop out and do not affect the transverse relaxation. (C) 1996 Academic Press. Inc.