QCPMG-MAS NMR of half-integer quadrupolar nuclei.

By combination of fast magic-angle spinning (MAS) and detection of the free-induction decay during a rotor-synchronized quadrupolar Carr-Purcell-Meiboom-Gill (QCPMG) train of refocusing pulses, the sensitivity of quadrupolar-echo MAS NMR spectra for the central transition of half-integer quadrupolar nuclei exhibiting large quadrupolar couplings may be significantly enhanced. Enhancements by an order of magnitude may easily be realized while maintaining information about the anisotropic interactions. In the present study the so-called QCPMG-MAS experiment is demonstrated experimentally and by numerical simulations for the two 87Rb sites in Rb2SO4.