An approach for enhancing the NMR sensitivity of the central transition of spin-3/2 nuclei is presented. Through selective excitation of the satellite transitions using a fast 180 degrees phase alternating pulse train during magic-angle spinning a selectively excited state is prepared where the populations of all eigenstates textbackslash m > with the same sign of m are equal, resulting in an enhanced central m = -1/2 --> 1/2 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-23 in Na2C2O4 and Rb-87 in RbClO4, respectively. We observe no significant anisotropic lineshape distortion. The conditions for optimum enhancement are discussed. (C) 2000 Published by Elsevier Science B.V.
Giovanni Boero, Fabio Donati, Soyoung Oh
Ellen Fogh, Sofie Janas, Paola Caterina Forino