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 angle spinning NMR spectrum of a spin-5/2 nucleus. Enhancement is achieved by fast phase alternation of the triple to single-quantum conversion pulse, which transfers triple to single-quantum coherence in a direct, non-adiabatic manner. The success of this pulse relies on the difference between the quadrupolar frequency and the intensity of the rf irradiation field, during its short segments. Numerical optimizations and experimental results are presented showing the improved performance.