Enhanced conversion of triple to single-quantum coherence in the triple-quantum MAS NMR spectrosocopy of spin-5/2 nuclei

A new type of fast amplitude modulated pulse scheme is presented here that yields a significant sensitivity enhancement in the triple-quantum magic an gle spinning NMR spectrum of a spin-5/2 nucleus. Enhancement is achieved by fast phase alternation of the triple to single-quantum conversion pulse, w hich transfers triple to single-quantum coherence in a direct, non-adiabati c manner. The success of this pulse relies on the difference between the qu adrupolar frequency and the intensity of the rf irradiation field, during i ts short segments. Numerical optimizations and experimental results are pre sented showing the improved performance. (C) 2000 Elsevier Science B.V. All rights reserved.