Solid State NMR at High Magnetic Fields Using Multiple Pulse Techniques

• Main Author: Carson, Douglas Glenn
• Format: Others
• Language: en
• Published: 1981
• Online Access: https://thesis.library.caltech.edu/4011/3/carson_dg_1981.pdf; Carson, Douglas Glenn (1981) Solid State NMR at High Magnetic Fields Using Multiple Pulse Techniques. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/172t-m550. https://resolver.caltech.edu/CaltechETD:etd-10102006-095702 <https://resolver.caltech.edu/CaltechETD:etd-10102006-095702>

<p>Part I of this thesis is concerned with measuring the proton chemical shift in solids using a homebuilt high field (6.3 tesla) multiple pulse spectrometer. The distinctive features of the spectrometer are described. The chemical shift tensors for the carboxylic protons in potassium hydrogen malonate, potassium hydrogen oxydiacetate, and potassium hydrogen dicrotonate are reported as determined by multiple pulse experiments. The isotropic part of the chemical shifts relative to a spherical sample of TMS and the anisotropies for the three compounds are -20.5(5), -19.6(7), -18.2(7), and 27.6(6), 28.3(9), 28.9(9) ppm respectively.</p> <p>Part II of this thesis presents a two pulse double quantum nuclear magnetic resonance (NMR) experiment which is designed to measure the Pake doublet splitting in systems of isolated proton pairs which are inhomogeneously broadened. This experiment is applied to the water molecules in the channels of a single crystal of cordierite as a function of orientation and temperature to obtain structural information about the water molecules. Based on the NMR data, the water molecules are found to exhibit substantial anisotropic motion at room temperature and combined with previously reported infrared absorption data, a two site hopping model is proposed where the water spends 85% of its time with its proton-proton vector parallel to the channels and 15% of its time perpendicular. The difference in free energy between these two sites is 0.8 kcal/mole.</p> <p>Average hamiltonian theory is extended to cover the case of strongly coupled proton-pair systems by transforming the hamiltonian to the dipolar pair-toggling reference frame. It is found that the residual dipolar hamiltonian for the Burum-Rhim 24-pulse cycle is governed by a four-body interaction and any other multiple pulse cycle based on phase alternated WAHUHA 4-pulse cycles will do no better than the 24-pulse cycle at reducing the residual dipolar hamiltonian.</p>