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

• Published in: Canadian journal of chemistry Vol. 89; no. 9; pp. 1055 - 1064
• Format: Journal Article
• Language: English
• Published: Ottawa NRC Research Press 01.09.2011; Canadian Science Publishing NRC Research Press
• Subjects: cinétique; Computer simulation; Coupling (molecular); dynamics of non-integer quadrupolar nuclei; dynamique des noyaux quadripolaires non entiers; déplacement quadripolaire résiduel du second ordre; Gas hydrates; glace-Ih; hydrate du clathrate du THF; Ice; ice-Ih; Injection; Kinetics; Melting; Molecular dynamics; molecular reorientations of solid water; Molecular structure; NMR; Nuclear magnetic resonance; O NMR; residual second order quadrupolar shift; RMN du; réorientations moléculaires de l’eau solide; Simulation; Tetrahydrofuran; THF clathrate hydrate
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v11-040

Lineshape analysis of 17 O 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 17 O 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 17 O nuclei. Lineshape analysis gave the quadrupolar coupling constant C Q  = 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 E a  = 55.2 ± 2.1 kJ mol –1 and E a  = 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.