QUASI-ADIABATIC POLARIZATION TRANSFER IN SOLID-STATE NMR

A modified Hartmann-Hahn type of cross-polarization experiment is performed with varying amplitudes of the radiofrequency field in a descending or ascending order. The initial spin state evolves quasi-adiabatically in a zero-quantum space to a final state with a larger polarization transfer than that under the matched Hartmann-Hahn condition, which is predicted by a spin flip-flop model to have the most efficient polarization transfer. Experimental results recorded for a sample of ferrocene powder agree qualitatively with the theoretical prediction. (C) 1994 Academic Press, Inc.