CROSS-POLARIZATION AT THE SLOW-CORRELATION LIMIT

The dynamics of cross polarization (CP) for rotating solids at the slow-correlation limit are described. The commonly used CP dynamic theory is invalid under these conditions because the dipolar-correlation time is the same order of magnitude as the cross-relaxation time. The oscillating behavior observed during CP and the asymmetric Hartmann-Hahn matching curve are satisfactorily explained by the theoretical treatment which we present. The effects of both zero- and double-quantum transitions on the efficiency of the CP process are considered. It is shown that under the experimental conditions, the spin temperature is not well defined both for rare and for abundant nuclei. The results of CP experiments performed under high-speed magic-angle spinning conditions demonstrate the correctness of the theoretical analysis presented. (C) 1994 Academic Press, Inc.