Sensitivity enhancement of the MQMAS NMR experiment by fast amplitude modulation of the pulses

We report here an improved way of doing the multiple-quantum magic-angle sp inning (MQMAS) NMR experiment that relies on the use of amplitude modulated pulses. These pulses were found to yield MQMAS NMR signals that an conside rably stronger (approximate to 200-300%) than the ones arising from the usu al continuous wave pulse schemes by virtue of a superior efficiency of the triple- to single-quantum conversion process. Numerical simulations and exp erimental results taking Na-23 and Rb-87 nuclei as examples are presented t hat corroborate the usefulness of this approach. (C) 1999 Elsevier Science B.V. All rights reserved.