Sensitivity enhancement of the central transition NMR signal of quadrupolar nuclei under magic-angle spinning

An approach for enhancing the NMR sensitivity of the central transition of spin-3r2 nuclei is presented. Through selective excitation of the satellite transitions using a fast 1808 phase alternating pulse train during magic-angle spinning a < : selectively excited state is prepared where the populations of all eigenstates m with the same sign of m are equal, resulting in an enhanced central msy1r2TM1r2 transition polarization. Numerical simulations predict enhancements up to a factor of 2 and values of 1.7 and 1.9 have been obtained experimentally for Na in Na C O and Rb in RbClO , respectively. 2 2 4 4 We observe no significant anisotropic lineshape distortion. The conditions for optimum enhancement are discussed. q 2000 Published by Elsevier Science B.V.