Low-Frequency Raman Scattering in a Xe Hydrate.

Thephysics of gas hydrates are rich in interesting phenomena suchas anomalies for thermal conductivity, self-preservation effects fordecomposition, and others. Some of these phenomena are presumablyattributed to the resonance interaction of the rattling motions ofguest molecules or atoms with the lattice modes. This can be expectedto induce some specific features in the low-frequency (THz) vibrationalresponse. Here we present results for low-frequency Raman scatteringin a Xe hydrate, supported by numerical calculations of vibrationaldensity of states. A number of narrow lines, located in the rangefrom 18 to 90 cm–1, were found in the Raman spectrum.Numerical calculations confirm that these lines correspond to resonancemodes of the Xe hydrate. Also, low-frequency Raman scattering wasstudied during gas hydrate decomposition, and two scenarios were observed.The first one is the direct decomposition of the Xe hydrate to waterand gas. The second one is the hydrate decomposition to ice and gaswith subsequent melting of ice. In the latter case, a transient low-frequencyRaman band is observed, which is associated with low-frequency bands(e.g., boson peak) of disordered solids. [ABSTRACT FROM AUTHOR]