High-resolution NMR spectra of nuclear spin systems under homogeneous interactions in solids exhibiting line narrowing induced by the memory effect

High-resolution nuclear magnetic resonance spectra of nuclear spin systems under strong homogeneous interactions in solids can be obtained simply by single-pulse excitation with a sufficiently long delay before data acquisition. The spectra are quantitative but subject to phase distortions. By inserting a refocusing pulse between excitation and acquisition, the sensitivity can be improved. The spectrum has the highest resolution when the sample is rotated at the magic angle, but the linewidth of the off-MAS spectrum does not show a P-2(cos beta) dependence. This method can be satisfactorily explained by means of memory-function theory, and many experimental results for static, magic-angle spinning, and off-magic angle spinning samples are presented. (C) 1995 Academic Press, Inc.