THE LOW-FREQUENCY VIBRATIONS IN CLATHRATE HYDRATES

The mechanism for the unexpectedly strong interactions between the gue st and lattice vibrations in clathrate hydrates is revealed from molec ular dynamics and lattice dynamics calculations on model systems, It i s shown that the vibrational couplings are the result of avoided cross ings of the enclathrated guest localized rattling modes with the host lattice acoustic phonon branches of the same symmetry. Through these c ouplings, energy can be exchanged between the host lattice and the gue st vibrations and lead to the anomalous glasslike behavior in the ther mal conductivity of gas hydrates. (C) 1997 American Institute of Physi cs.