PULSED-FIELD GRADIENT SELECTION IN 2-DIMENSIONAL MAGIC-ANGLE-SPINNINGNMR-SPECTROSCOPY OF DIPOLAR SOLIDS

The utility of gradient selection in MAS spectroscopy of dipolar solid s is explored in two examples. In the first, rotor-synchronized gradie nts of appropriate strength and duration are applied to select H-1 dou ble-quantum coherences. The resulting DQ MAS spectrum of adamantane is compared with that acquired by the corresponding phase-cycling techni que, As a second example, a H-1 2D exchange MAS experiment is performe d on an elastomer sample. In this experiment, a gradient is applied to remove undesired coherences that would otherwise distort the spectrum for short mixing times. The diagonal-peak intensities in the resultin g spectrum show a linear decrease with increasing mixing time indicati ng cross-relaxation by slow chain motions as the relevant process. Bot h types of experiments demonstrate the potential of gradient-selection techniques for MAS spectroscopy of dipolar solids. (C) 1998 Academic Press.