ENHANCEMENT OF POLARIZATION TRANSFER UNDER HIGH-SPEED MAS USING A QUASI-ADIABATIC CROSS-POLARIZATION SEQUENCE

A quasi-adiabatic cross-polarization sequence, with varying amplitudes of the radiofrequency field in a descending or ascending order, is used under high-speed MAS conditions to achieve a more efficient polarization transfer. It partially inverts the populations between the two energy states in a zero-quantum space for an IS-coupled system instead of equalizing the populations, as does the conventional Hartmann-Hahn cross-polarization sequence under the matched conditions. The quasi-adiabatic cross-polarization sequence is also quite insensitive to the match conditions and the MAS speed. (C) 1994 Academic Press, Inc.