Spontaneous Raman Spectra And Metastable Phase Of Shock-compressed Water

Water is one of the most abundant substances in nature, and it has important applications in industry and in national defense. The structure of a single molecule is simple, but its condensed form is diverse and complex. Under static compressions, more than 10 kinds of ice with different structures have been found. However in the dynamic loading process, people know little about the structural transformation of water. The dynamic loading by shock wave usually occurs on the time scale of nanoseconds, during which the temperature and the pressure of the condensed system may change more quickly than the phase transformation, so that the structure of the system will evolve directly into some metastable forms instead of the normal crystallization as observed under the static compression. Structural evolution of water during shock compression will change its dynamic behaviors, which are the necessary physical and mechanical parameters when the attack and protection schemes of the underwater targets are designed. In recent years the isentropic and quasi-isentropic (reverberation) loading techniques were applied to research the dynamic properties and optical transparency of water, the phenomena of shock-induced freezing and phase transformation relaxation were observed. It should be pointed out that the shock-induced crystallization is still an indirect speculation, since the investigations of microscopic structure and spectral characteristics of the high-pressure ice face technical challenge. Spontaneous Raman spectra technique is the ideal tool to testify the shock-induce structural transition, unfortunately, the Raman signal is found to be very weak because of the small scattering cross section of water molecule, and such a technical bottleneck has not been breakthrough for thirty years.In the thesis, a spontaneous Raman spectra technique based on gas-gun loading condition is developed, in which the precision of time control and spectral sensitivity are obviously improved, and it is capable of tracking the multiple reverberation loading processes and resolving the more abundant spectral features of shocked water. The shock compression platform of two-stage light-gas gun and the spontaneous Raman technique of in-situ spectroscopy, together with ab initio MD method, are adopted to reveal the microscopic structure, vibration spectrum, and hydrogen-bonding effects of shock-compressed water. Some innovative conclusions are summarized as follows:(1) By shock and re-shock loading schemes the spontaneous Raman spectra of shocked water is firstly obtained in the phase region near the melting curve of ice Ⅶ respectively at liquid and solid sides; (2) During the compression of re-shock the lower wavenumber component in Raman spectra of shocked water is found to rise for the first time, and it demonstrates that hydrogen-bonding effects become stronger; (3) The spontaneous Raman spectra of shocked water at phase region of ice Ⅶ is firstly observed, it reveals that the new phase generated by shock-induced freezing is different from the expected ice Ⅶ, but a metastable phase; (4) By ab initio MD method an amorphous ice is found at high pressure and temperature, it reveals that the new disorder system has wide O-H stretching vibrational spectrum which is similar with the observed Raman spectrum; (5) By ab initio MD method the dependence of O-H vibration spectrum on the length of the hydrogen bond is firstly revealed, and the results support the viewpoint that asymmetrical O-H stretching vibration spectrum is ascribed to the asymmetry of hydrogen-bonding environment.