Composite pulses for efficient excitation of half-integer quadrupolar nuclei in NMR of static and spinning solid samples

Abstract

Composite pulses of the type (τp)x(2τp)-x(3τp)x allow one to excite the central transition of nuclei with half-integer spin with enhanced efficiency compared to a simple (τpsp)x pulse. The method has been tested on solid samples containing sodium-23 (I=3/2), aluminium-27 (I=5/2) and scandium-45 (I=7/2) under both static and magic-angle spinning conditions. Numerical simulations for I=3/2 indicate that the enhancement is due to a more efficient conversion of Zeeman population differences associated with the satellite transitions to the central transition.