Date Awarded
1996
Document Type
Dissertation
Degree Name
Doctor of Philosophy (Ph.D.)
Department
Physics
Advisor
Gina L Hoatson
Abstract
Deuteron NMR selective inversion (SI) is developed to study slow molecular motions in solids. Theoretical and practical aspects of selective inversion of spin-1 nuclei in solids are presented. Differences between powdered solids and liquids are considered. Double sideband modulated (DSBM) shaped pulses are shown to improve the performance of SI pulses. DSBM and DANTE selective pulses are compared for off-resonance SI applications. Common spin-{dollar}{lcub}1{rcub}\over{lcub}2{rcub}{dollar} shaped pulses are tested for suitability to solid state deuteron NMR. Simple, short pulses are shown to be most effective due to fast spin-spin relaxation and large underlying homogeneous linewidths in solids.;The power and utility of selective inversion is demonstrated by investigating the molecular dynamics of polycrystalline dimethylsulfone-{dollar}\rm d\sb6{dollar} (DMS). Quantitative information on the slow two-site jump motion in DMS is obtained. The complementary nature of selective inversion and quadrupolar echo lineshape (QELS) experiments is explored. Combination of QELS and SI extends the range of rates observed, increasing the accuracy of the information obtained. For DMS, motional rates were measured over a 80 K range (motional rates of {dollar}\rm 3\times 10\sp1{lcub}-{rcub}5\times 10\sp{lcub}4{rcub}\ s\sp{lcub}-1{rcub}),{dollar} permiting the barrier to slow rotation to be accurately characterized. SI was also used to observe the limiting homogeneous linewidth as a function of resonance offset and temperature. The temperature dependence of the homogeneous linewidth is shown to be sensitive to motion in the kilohertz range.;SI was used to quantify the molecular dynamics in some complex systems. SI and QELS experiments were performed on host urea-{dollar}d\sb4{dollar} in different urea inclusion compounds (UIC). Rotation rates about both the CO and CN bonds of urea-{dollar}d\sb4{dollar} in the UICs were determined as a function of temperature. Activation energies were obtained, and the results are discussed with respect to guest-host interactions in the UICs. Preliminary results are presented on quadrupolar echo lineshape simulations which include empirical, anisotropic homogeneous linewidth corrections. The modified simulations give significantly different best-fit motional rates than conventional QELS analysis. This allows some of the systematic errors of QELS analysis to be evaluated.;SI experiments were conducted, over a 125 K range, to study backbone motion in bisphenol-A polycarbonate. These experiments failed to detect the presence of any large angle slow motion of methyl groups in the isopropylidene moiety. This negative result suggests that cis-trans isomerization of the carbonate group is not the origin of the backbone motion.
DOI
https://dx.doi.org/doi:10.21220/s2-s64b-m146
Rights
© The Author
Recommended Citation
Brown, Marco J., "Selective inversion in solid-state deuteron NMR" (1996). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539623900.
https://dx.doi.org/doi:10.21220/s2-s64b-m146
