No abstract

The thermal conductivity of a gas hydrate is much lower than that of ice and more intriguingly, in spite of the crystalline structure, the temperature profile resembles an amorphous solid. Here we present results from neutron incoherent inelastic scattering (IINS) experiments and theoretical relaxation time calculations to demonstrate unambiguously the coupling of guest and water framework vibrations. The coupling is the consequence of symmetry forbidden crossings of the localized guest motions with the acoustic branches of the lattice vibrations. This phonon interaction leads to an energy exchange mechanism that explains the anomalous thermal behaviour.

No abstract

The mechanism for the unexpectedly strong interactions between the guest and lattice vibrations in clathrate hydrates is revealed from molecular dynamics and lattice dynamics calculations on model systems. It is shown that the vibrational couplings are the result of avoided crossings of the enclathrated guest localized rattling modes with the host lattice acoustic phonon branches of the same symmetry. Through these couplings, energy can be exchanged between the host lattice and the guest vibrations and lead to the anomalous glasslike behavior in the thermal conductivity of gas hydrates.