Studies on the Phonon Dynamics and Structural Phase Transitions in Clathrate Hydrates by Raman and X-ray Scattering

The purpose of this research is to study The phonon dynamics and structural phase transitions inclathrate hydrates. In particular，we are interested in the changes of the hydrogen bonds of水分子upon the transitions andthe molecular field around the guest molecule.Firstwater solusion of fullerol c_ <60> (oh_x is studied. The solution is found, however，to contain some chemical impurities such as naoh and t e t rabutylammoniumhydroxide . though,at this time, we are not successful in completely characterizing the samples，we hope to purify c_ <60> （oh_x and conduct more quantitative experiments on the fullerol clathrate）hydrate system.second,tetrahydrofuran (THF) clathrate hydrate and liquid THF 17h_2o are studied by Raman spectroscopy.From the frequencies of O-H vibrations as well as the hydrogen bond vibrations，我们suggest that the strength of the h_2o host network in liquid THF 17h_2o is about the same as thatin water. Upon the formation of the hydrate，the h_2 host network becomes stronger. the frequencies of the C-O-C and ch_2 vibrations of THFmolecules in THF hydrate are found to be higher than in pure THF liquid. The depolarization ratiosof the C-O-C symmetric and asymmetric stretching vibrations vary drastically as the THF moleculesare in different physical states, such as in pure THF liquid, in liquid water，在hydrate的cages of the hydrate.我们希望在THF hydrate更多类似于自由的THFmolecule in the gas phasefive-member ring of THF molecule is buckled. five-member ring of THF molecule isplanar when THF is liquid THF 17h_2 . an Ag-like mode at 900cm <-1>，which is not observable in either pure water or pure THF liquid，is observed in the Raman spectra of liquid THF 17h_2o and THF hydrate。

The purpose of this research is to study the phonon dynamics and structural phase transitions in clathrate hydrates. In particular, we are interested in the changes of the hydrogen bonds of water molecules upon the transitions and the molecular field around the guest molecule.First, water solusion of fullerol C_<60> (OH) _X is studied. The solution is found, however, to contain some chemical impurities such as NaOH and tetrabutylammoniumhydroxide. Though, at this time, we are not successful in completely characterizing the samples, we hope to purify C_<60> (OH) _X and conduct more quantitative experiments on the fullerol clathrate hydrate system.Second, tetrahydrofuran (THF) clathrate hydrate and liquid THF・17H_2O are studied by Raman spectroscopy. From the frequencies of O-H vibrations as well as the hydrogen bond vibrations, we suggest that the strength of the H_2O host network in liquid THF・17H_2O is about the same as that in water. Upon the formation of the hydrate, the H_2O host network becomes stronger. The frequencies of the C-O-C and CH_2 vibrations of THF molecules in THF hydrate are found to be higher than in pure THF liquid. The depolarization ratios of the C-O-C symmetric and asymmetric stretching vibrations vary drastically as the THF molecules are in different physical states, such as in pure THF liquid, in liquid water, and in the cages of the hydrate. We suggest that THF molecule in THF hydrate is more like a free THF molecule in the gas phase, in which the five-member ring of THF molecule is buckled. The five-member ring of THF molecule is more planar when THF is liquid THF・17H_2O.An Ag-like mode at 900cm^<-1>, which is not observable in either pure water or pure THF liquid, is observed in the Raman spectra of liquid THF・17H_2O and THF hydrate.