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

Composite pulses of the type ( τ p ) x ( 2 τ p ) - x ( 3 τ p ) x allow one to excite the central transition of nuclei with half-integer spin with enhanced efficiency compared to a simple ( τ p sp ) 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.