| dc.description | Nuclear magnetic resonance (NMR) spectroscopy of solids has become widely used in the study of a great variety of solid materials. However, new observations are still emerging and many spectral properties are not well-understood, even for simple spin-pair systems consisting of two homonuclear spin-${1\over2}$ nuclei. This thesis represents a detailed investigation of NMR spectra arising from homonuclear two-spin systems in both static and rotating solids. The great potential of the dipolar-chemical shift NMR method in characterizing chemical shift tensors is demonstrated for static solids. Using this method, chemical shift tensors involving $\sp $C, $\sp $N and $\sp{31}$P nuclei have been determined in various classes of compounds of chemical interest. Some of the compounds investigated exhibit NMR spectra with interesting features which had not been reported previously. It is found that the observed anomalous features could be interpreted as arising from second-order (AB) effects. Based on average Hamiltonian theory, a uniform treatment is developed for interpreting various new observations concerning spinning-frequency dependent phenomena observed in magic-angle-spinning (MAS) NMR spectra of rotating solids. Under slow MAS conditions, factors that determine the resolution limit in MAS NMR spectra arising from two dipolar-coupled spins are studied and the relationships between crystallographic equivalence and MAS NMR spectra are also investigated. Two new applications of variable-angle-spinning (VAS) NMR experiments are demonstrated. It is found that spinning a sample rapidly about an axis other than the magic angle provides a new method for reintroducing J coupling between two crystallographically equivalent but magnetically non-equivalent spins. A particular significance of the VAS method is that it yields information concerning the relative orientation between the chemical shift tensors of two J-coupled spins. The VAS method will be useful to systems where the dipolar-chemical shift NMR method is not applicable. | en_US |
