Theory of Quadrupolar Spins Line Narrowing Techniques

THEORY OF QUADRUPOLAR SPINS LINE NARROWING TECHNIQUES 

A typical MQMAS spectmm is shown in Fig. 2. The 2D spectrum is a MQMAS Rb spectmm of a sample of mbidium nitrate clearly showing the three well-resolved Rb sites. The Fj projection shows the isotropic spectmm and the projection shows the MAS anisotropic spectmm. The slices across the 2D contours give the anisotropic lineshape of each of the sites. An analysis ofboth these projections (and the anisotropic lineshapes) aided by numerical methods yields the isotropic chemical shift and the quadmpolar interaction parameters of Rb in this sample. 

In the following, we show how an MQMAS echo is formed. The quadmpolar Hamiltonian under MAS will be derived as a perturbation to the strong static magnetic field Bq. The evolution of the density matrix under this Hamiltonian will be then shown to form an echo under a suitable selection of symmetric coherences. The manipulation of spin coherences by RF pulses will be assumed to be ideal here. The effects of nonidealities were discussed by the group of Vega. From the expression for the elements of the quadmpolar Hamiltonian, line narrowing by DOR experiment and echo formation by two alternative experiments, DAS and STMAS, will also be demonstrated and briefly discussed. Finally, some additional line narrowing schemes will be mentioned. 

Since we will be discussing only the echo formation, for details regarding the MAS spectra and expressions of the NMR lineshapes of quadrupolar nuclei, the reader is directed to some excellent reviews concerning quadmpolar nuclei by Freude, Smith and VanEck, Man, Frydman, and Kentgens. Additional reviews of interest on MQMAS include those of Amoureux and Pmski, and Goldbourt and Madhu.  

Zeeznan+quadrupolar interaction, first order and second order 

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Theory of Quadrupolar Spins Line Narrowing Techniques... 

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