NUTATION MAGIC-ANGLE-SPINNING SPECTRA OF HALF-INTEGER QUADRUPOLE SPIN SYSTEMS

The nutation spectra of spin-3/2 and spin-5/2 nuclei under magic-angle spinning (MAS) were investigated in detail. When the nutation time is larger than a spinning period, the lineshape of a nutation spectrum is evidently changed by MAS. The center of gravity of the nutation MAS spectrum is generally shifted to lower frequency compared with the static spectrum. The shift is approximately inversely proportional to the spinning speed. When the effective quadrupole coupling constant is much larger than the irradiation field amplitude, the nutation spectra are broadened by MAS, while if the effective quadrupole coupling constant is much smaller than the RF field amplitude, the nutation spectra are generally narrowed by MAS. For certain values of the effective quadrupole coupling constant, the nutation spectrum may exhibit a minor dispersion. For a nutation time shorter than one spinning period, the lineshape is similar to that in the static case. A natural and exact computation approach for theoretical spectral simulation is presented, and the necessity for phase correction of theoretical spectra is discussed. The experimental results are in good agreement with theoretical simulations. (C) 1995 Academic Press, Inc.