Water molecular reorientation in ice and tetrahydrofuran clathrate hydrate from lineshape analysis of 17O spin-echo NMR spectra

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DOIResolve DOI: http://doi.org/10.1139/v11-040
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TypeArticle
Journal titleCanadian Journal of Chemistry
Volume89
Issue9
Pages10551064; # of pages: 10
Subjectice-Ih, THF clathrate hydrate, 17O NMR, molecular reorientations of solid water, Kinetics, residual second order quadrupolar shift, dynamics of non-integer quadrupolar nuclei
AbstractLineshape analysis of 17O spin-echo NMR spectra has been used to study water molecular reorientations in ice-Ih and THF Structure II clathrate hydrate. The kinetics was determined by the changes of the lineshapes of the 17O central transitions at different temperatures. A model involving 12 orientations and 4-step jumps of water molecular orientations was proposed. Semi-classical exchange formalism was employed to simulate the lineshape of the central transitions of the 17O nuclei. Lineshape analysis gave the quadrupolar coupling constant CQ = 6.43 MHz and the asymmetry parameter η = 0.935, for both ice-Ih and THF gas hydrate. The theoretical lineshape simulations resulted in activation energies of water molecular reorientations Ea = 55.2 ± 2.1 kJ mol–1 and Ea = 30.5 ± 0.8 kJ mol–1 for ice-Ih and THF hydrate, respectively. The range of dynamic rates in THF clathrate hydrate is such that before melting, a pseudo-isotropic lineshape is observed that retains a second-order quadrupolar shift. The water reorientation process is discussed in light of recent results on Bjerrum defect injection obtained from molecular dynamics simulation and structural studies.
Publication date
LanguageEnglish
AffiliationNRC Steacie Institute for Molecular Sciences; National Research Council Canada
Peer reviewedYes
NPARC number19727323
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Record identifier07809cc3-4a2b-406a-b0c3-4588165f0ded
Record created2012-03-29
Record modified2016-05-09
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