Modulation-aided signal enhancement in the magic angle spinning NMR of spin-5/2 nuclei

We report signal enhancement schemes using fast amplitude modulated pulses for the one-dimensional (1D) nuclear magnetic resonance (NMR) of spin-5/2 nuclei under magic-angle spinning. Signal enhancement by a factor of around 2.5 is observed when amplitude modulated pulses precede selective excitation of the central transition. This enhancement is a result of the redistribution of energy level populations through partial saturation of the satellite transitions. Results are shown for 27Al and 17O. The gain in signal intensity is very useful for the observation of weak signals from low abundance quadrupolar nuclei. The scheme works for wide ranges of quadrupole interactions and rf powers.