2-DIMENSIONAL SPIN-ECHO DIPOLAR-SIDE-BAND ENHANCEMENT IN MAGIC-ANGLE-SPINNING NMR

A series of new two-dimensional dipolar-chemical-shift experiments in magic-anglespinning NMR are presented. A π pulse applied in the center of the evolution period produces dipolar sidebands spaced at one-half the spinning frequency in the ω1 dimension. The π pulse may be applied to either rare or abundant spins, with differing results upon the spectrum. In both cases the sidebands are more intense than those obtained by conventional methods and should assist the measurement of small heteronuclear dipolar couplings. For one experiment, a dipolar spectrum may be extracted from the 2D landscape which is rigorously identical to the dipolar spectrum at one-half the actual spinning speed. The 2D sideband arrays are sensitive to the relative orientation of the chemical-shift and dipolar tensors, even in the regime where the spinning rate is comparable to the size of one or both tensors. © 1991.