Abstract:

 A Raman microspectrometer combined with a Linkam heatingfreezing stage was used to acquire Raman spectra of fluids in a H2OCO2 system in optical fused silica capillary sample at the temperature from -120 ℃ to 31 ℃ and in the 1200 and 1500 cm-1 regions. The results show that the fluids in fused silica capillary are the representative of loading fluids. Through the acquisition of Raman spectra of fluids in capillary, the Raman spectra of vapor CO2, liquid CO2, solid CO2, CO2 hydrate and CO2 in aqueous solution in fluid inclusion are characterized. These spectra reveal that the characteristic peak positions in solid CO2 and CO2 hydrate spectra are stable in the range of experimental temperature, which is helpful in identifying the bands in Raman spectra, and that the Fermi resonance peak positions of the spectra of vapor CO2, liquid CO2 and CO2 in aqueous solution are changed with the variation of pressure or the density of CO2. This study also analyzed the Raman spectra of different phases at different temperatures, which indicates that the technique of Raman microspectroscopy combined with microthermometry can effectively identify the different phases in fluid inclusions, catch on the process of phase changes, and determine the temperatures of phase changes.

Key words:  H2O-CO2 system, optical fused silica capillary, Raman spectroscopy, solid CO2, CO2 in aqueous solution