Electronic and Vibratonal Properties of Gas Hydrates

INTRODUCTION The most unique physical property of gas hydrate is the anomalous low and unexpected glassy-like thermal conductivity [ I ,2]. This interesting behaviour has both significant practical and scientific consequences. Thermal conductivity is a vital parameter required for the computer modelling of the recovery of natural gas from the hydrate [3]. A knowledge on the variation of the thermal conductivity with pressure and temperature is a prerequisite to the exploitation of this important natural resource. Despite the well defined crystalline structures for gas hydrates [4,5], their thermal conductivities are characteristic of amorphous materials. The understanding of the causes responsible for this unusual phenomenon will sled light on the mechanism of thermal transport in the disorder system. In solid, the thermal energy is transported and dissipated by the acoustic lattice vibrations. These vibrations are normally too low in energy to be effectively studied by infrared and Raman spectroscopy. However, they can be conveniently probed by neutron incohorent inelastic spectroscopy. In the following, the results from such measurements will be presented and discussed with the aid of computer simulation of the guest and lattice vibrations with lattice dynamics and molecular dynamics methods.