Strange effects of pulse shaping in water presaturation experiments
During the course of some water presaturation experiments with a shaped pulse envelope we observed inverted responses from certain signals flanking the water response. This phenomenon did not occur when a rectangular presaturation envelope was used. Apparently the leading and trailing edges of the shaped pulse act as adiabatic sweeps, causing the coupled magnetizations in question to be spin-locked. This gives rise to Hartmann-Hahn coherence transfer, and when the spin lock duration is equal to 1/(2J) the trajectories are such as to carry these magnetization vectors to the -z axis, leading to inverted signals in the final spectrum. Copyright 2000 Academic Press.
Kupce
E
Varian NMR Instruments, 28 Manor Road, Walton-on-Thames, Surrey, KT12 2QF, England.
Freeman
R