LOCAL-FIELD MEASUREMENTS ON POWDER SAMPLES FROM POLARIZATION INVERSION OF THE RARE-SPIN MAGNETIZATION

A simple two-dimensional procedure is used to obtain chemical-shift-dipolar-correlated spectra for static or magic-angle spinning powder samples. The polarization inversion of the S-spin magnetization during t1 is used to introduce dipolar evolution as a modulation of the chemical-shift domain t2. This permits a large spectral width in the unscaled dipolar dimension and does not require synchronization with the macroscopic rotation. For a static or slowly rotating sample of ferrocene, there is good agreement between experimental and calculated line-shapes which permits visualization of coherent energy transfer effects and the expected coincidence of the two tensors in the presence of fast internal rotation. A slowly spinning experiment as well as a spin-echo experiment with dipolar modulation shows that, in analogy to the particular chemical-shift position for a stationary sample, each particular spinning sideband in the slow-spinning regime or peak in the spin-echo spectrum represents respectively a narrow range of orientations or a particular orientation of crystallites with respect to the magnetic field. Other examples of dipolar local-field measurements for rapidly spin-fling samples are presented in more typical organic solids. © 1993 by Academic Press, Inc.