CROSS-POLARIZATION FROM QUADRUPOLAR NUCLEI TO SILICON USING LOW-RADIO-FREQUENCY AMPLITUDES DURING MAGIC-ANGLE-SPINNING

The dynamics of cross-polarization from the central transition of a qu adrupolar nucleus (Al-27 or Na-23) to a spin-1/2 nucleus (Si-29) durin g magic-angle spinning and using low-radio-frequency Geld strengths ar e analyzed for the mineral low albite. Under these conditions addition al complications in the spin-lock behavior of the quadrupolar nucleus and in the cross-polarization process were found experimentally and ar e examined in detail. A step-by-step procedure for optimizing cross-po larization from the central transition of a quadrupolar nucleus to a s pin-1/2 nucleus is described. Significant enhancement of Si-29 NMR sen sitivity and several applications are demonstrated.