Multiple quantum NMR spectroscopy onI> 1 nuclei in anisotropic systems

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Abstract
The response of half-integral spin I > 1 nuclei in anisotropic systems to pulse sequences exciting multiple quantum (MQ) coherences is investigated theoretically. Using the state multipole formalism, we calculate the 2-dimensional (2D) MQ spectrum obtained by the conventional three-pulse sequence and compare it to recent experimental results. Next we consider MQ filters for detecting the evolution of rank (2I - 1) single quantum coherences. Pulse sequences based on these filters can be used for revealing hidden anisotropy in a spectrum or for suppressing a dominant isotropic contribution. Finally, we develop 2D spinecho and quadrupolar echo experiments that refocus the inhomogeneous decay of various MQ coherences. These MQ echo techniques can be used to determine accurately the homogeneous line widths of various MQ transitions, as demonstrated by experimental results (including the first MQ quadrupolar echo spectra) on 23Na and 17O nuclei in a lyotropic liquid crystal.