THEORETICAL CALCULATIONS OF THE CPMAS SPECTRAL LINESHAPES OF HALF-INTEGER QUADRUPOLE SYSTEMS

An exact formalism to permit calculation of the spectral lineshapes arising from cross polarization (CP) between protons and a half-integer quadrupole system under magic-angle spinning (MAS) is described. The distortions of CPMAS spectra for different contact times, under different matching conditions, were satisfactorily explained by numerical computations. The cross-relaxation effect on spectral lineshape was considered. Moreover, the CPMAS and static CP spectra are compared and it is shown that the distortion of the CPMAS spectrum is not necessarily more severe than that of the static CP spectrum. The formalism presented in this work makes possible the extraction of quadrupolar parameters from a distorted CPMAS or a static CP spectrum. (C) 1995 Academic Press, Inc.