N-14 nuclear magnetic resonance of polycrystalline solids with fast spinning at or very near the magic angle

The N-14 nuclear magnetic resonance spectra of polycrystalline samples of K NO3, NH4NO3, and several amino acids have been studied under the condition of magic angle spinning. These compounds have N-14 quadrupolar coupling con stants of about 1 MHz, but it is possible to obtain peaks with linewidths o f a few hundred Hz and good signal/noise ratio. The spectra contain informa tion on both isotropic chemical shifts and quadrupolar coupling constants. The effect of very small deviations from the magic angle (less than or equa l to 0.05 degrees) is studied, and the corresponding spectral features are analyzed qualitatively and quantitatively. The use of a weak pulse or a wea k composite pulse causes an increase in the signal intensity, and an analys is is given to explain these unusual results. (C) 1999 American Institute o f Physics. [S0021-9606(99)00143-9].