19F SPEDA NMR spectra in rotating solids

High resolution 19F NMR spectra of rotating polycrystalline solids can be obtained by single pulse excitation with a long delay before acquisition (SPEDA). However, the overall spectral range is influenced by the chemical shift anisotropy which, unlike the situation for protons, might be large for 19F nuclei. Three typical cases can be distinguished according to the relative magnitudes of the chemical shift anisotropies and homonuclear dipolar interactions. The second-order effect arising from the non-commutability of the chemical shift and homonuclear dipolar interactions is discussed. The linewidths of the central bands and the characteristics of the sidebands are analyzed. It is found that Anderson-Weiss approximation of the memory equation must be modified to explain the sideband phenomena observed.