Multiple-quantum MAS NMR spectroscopy of spin-3/2 quadrupolar spin systems using shaped pulses.

An investigation of the effect of shaping the pulses in multiple-quantum magic-angle nuclear magnetic resonance experiments was carried out on polycrystalline samples containing spin-32 quadrupolar nuclear spins. Both theoretical analysis and numerical simulations show that there exist types of shaped pulses that are more advantageous than the usual rectangular pulses in exciting multiple-quantum coherences and converting these into single-quantum coherences or zero-quantum coherences (in z-filtering cases). The sensitivities can be enhanced without loss of resolution or increasing the RF offset dependences. Moreover, properly shaped pulses can moderate the requirements on the RF power and sample spinning speeds. Especially important for application purposes is the finding that lattice site quantification can also be improved by the use of certain shaped pulses.