Raman spectra of structure I methane hydrate under different pressures.

We report on a set of Raman spectra of structureⅠmethane hydrates under pressures of 132～901MPa and 25℃. Methane hydrate samples were synthesized with small granular ices as‘seed'and pure methane,under a pressure of 18 MPa and changing temperature from 0℃to 9℃for about 2 days.The samples were observed with microscopy and in situ measured with Raman Spectroscopy in a diamond anvil cell.The result showed that the Raman spectra of samples were doublets with left peak positions of 2904.4～2907.2cm~(-1) and fight peak positions of 2915～2922cm~(-1).shifted to higher wavenumbers with increasing pressures.The typical intensity ratio of the doublets was about 3:1,which is as characteristics of structureⅠ.That means that methane hydrate can maintain structureⅠup to a high pressure.Also Ramam spectra for methane dissolved in water and methane in gas phase were measured under a pressure of about 170MPa and 25℃,which were obviously different to the Raman spectra of structureⅠmethane hydrate samples.