Shaped pulse excitation in multi-quantum magic-angle spinning spectroscopy of half-integer quadrupole spin systems

Coherence excitation by shaped pulses in the multi-quantum magic-angle spinning spectroscopy of half-integer quadrupole spin systems was explored. A theoretical analysis shows there exists a class of shaped pulses that are superior to the rectangular pulses normally used in MQMAS studies. Significant sensitivity enhancement can be achieved without loss of resolution and quantification. This is verified by numerical simulations based on decaying triangular and exponential shaped pulses. 23Na multi-quantum magic-angle spinning spectra of polycrystalline anhydrous di-sodium hydrogen phosphate (Na2HPO4) are shown to be well-explained by the theoretical analysis.