Transient Translational and Rotational Water Defects in Gas Hydrates

We report our observations of the transient formation of the translational and rotational defects in the host lattice of methane hydrates. We perfortn molecular dynamics simulations of a fully occupied methane hydrate system and find that the hydrogen bonds of a water molecule can be thermally broken, and the water molecule can: then rotate more freely. We observe the formation of transient Bjerrum defects around, the water: molecule, and the two hydrogens of the water molecule can be interchanged when the transient defects anneal. The 95% confidence interval for the rate of the hydrogen interchange is estimated to be 1.3 X 10(5)-2.4 X 10(5) s(-1) per water molecule, and the 95% confidence interval for the associated free energy of activation is estimated to be 38.2-39.4 kJ/mol at 270 K. We also observe the transient formation of vacancy-interstitial water defects. The, formation and annealing of these vacancy-interstitial defects can result in the interchange of two or three neighboring water molecules on the gas hydrate lattices. The 95% confidence interval for the rate of the formation of transient vacaney-interstitial water defects as a result of the water interchanges is estimated to be 6.7 x 10(2)-1.6 X 10(4) s(-1) per water molecule and. the 95% confidence interval for the associated free energy of activation is estimated to be 44.1-51.3 kJ/mol at 270 K.