Multiple quantum magic-angle spinning using rotary resonance excitation

We have discovered rotary resonances between rf field strength, omega (1), and magic-angle spinning (MAS) frequency, omega (R), which dramatically enh ance the sensitivity of triple quantum preparation and mixing in the multip le-quantum MAS experiment, particularly for quadrupolar nuclei having low g yromagnetic ratios or experiencing strong quadrupole couplings. Triple quan tum excitation efficiency minima occur when 2 omega (1) = n omega (R), wher e n is an integer, with significant maxima occurring between these minima. For triple quantum mixing we observe maxima when omega (1) = n omega (R). I n both preparation and mixing the pulse lengths required to reach maxima ex ceed one rotor period. We have combined these rotary resonance conditions i nto a new experiment called FASTER MQ-MAS, and have experimentally demonstr ated a factor of 3 enhancement in sensitivity in comparison to conventional MQ-MAS. (C) 2001 American Institute of Physics.