Sm. De Paul et al., Sideband patterns from rotor-encoded longitudinal magnetization in MAS recoupling experiments, J MAGN RES, 146(1), 2000, pp. 140-156
Recent multiple-quantum MAS NMR experiments have shown that a change in the
rotor phase (and, hence, in the Hamiltonian) between the excitation and re
conversion periods can lead to informative spinning-sideband patterns. Howe
ver, such "rotor encoding" is not limited to multiple-quantum experiments.
Here it is shown that longitudinal magnetization can also be rotor-encoded.
Both homonuclear and heteronuclear rotor encoding of longitudinal magnetiz
ation (RELM) experiments are performed on dipolar-coupled spin-1/2 systems,
and the corresponding sideband patterns in the indirect dimension are anal
yzed. In both cases, only even-order sidebands are produced, and their inte
nsity distribution depends on the durations of the recoupling periods. In h
eteronuclear experiments using REDOR-type recoupling, purely dipolar sideba
nd patterns that are entirely free of effects due to the chemical-shielding
anisotropy can be generated. Advantages and disadvantages of the heteronuc
lear RELM experiment are discussed in the context of other methods used to
measure heteronuclear dipolar couplings. (C) 2000 Academic Press.