Abstract

       Solid-state NMR spectra of quadrupolar nuclei are often poorly resolved due to the presence of anisotropic second-order quadrupolar broadening, even under conventional magic angle spinning (MAS) conditions. The two-dimensional multiple-quantum MAS (MQMAS) experiment is one of several techniques which have been designed to remove this broadening and provide high-resolution NMR spectra of half-integer quadrupolar nuclei. This thesis demonstrates that, in the absence of this pure quadrupolar broadening, it is possible to observe a weak quadrupolar-dipolar interaction which also survives conventional MAS and is the result of dipolar coupling to nearby quadrupolar nuclei.

       Perturbation theory is used to describe this quadrupolar-dipolar broadening and predict the lineshapes observed in MQMAS and other high-resolution spectra. Furthermore, measurements at multiple magnetic field strengths unambiguously identify the quadrupolar-dipolar broadening. The coupling of quadrupolar and chemical shift anisotropy interactions is also shown to lead to broadening in the satellite transitions of quadrupolar nuclei. Systems in which the quadrupolar interaction is very strong are investigated and shown to be poorly described by perturbation theory expressions. Instead, exact numerical diagonalization methods are used to give a theoretical description of the quadrupolar-dipolar broadening in such cases.

       As a high-resolution technique, the MQMAS experiment has also been applied to the study of amorphous materials. The spectra of these compounds show significant additional broadening due to the presence of distributions of chemical shift and quadrupolar parameters. A lineshape-fitting routine is proposed, tested and applied to obtain quantitative estimates of these distributions in the 27Al MQMAS NMR spectra of a series of amorphous aluminosilicate compounds.