Raman vibrational spectral characteristics and quantitative analysis of H₂ up to 400°C and 40 MPa

In situ Raman detection is an ideal method to determine the concentration of dissolved H₂ in deep-sea high temperature hydrothermal fluids, but studies on in situ Raman qualitative and quantitative analyses of H₂ that are suitable for detection in high temperature hydrothermal fluids are lacking. In this study, the Raman characteristics of gaseous and dissolved H₂ were researched at 0–400°C and 0–40 MPa in detail, which cover most deep-sea hydrothermal environments. The strong density and temperature dependences of the wavenumber and bandwidth of gaseous hydrogen vibrational Raman bands were observed. The interactions between the water molecules and hydrogen molecules were affected by temperature and pressure, and the opposite effect on the vibrational band of dissolved hydrogen was observed before and after reaching the critical condition of water. A high temperature and pressure quantitative analysis model suitable for in situ Raman detection of dissolved H₂ was also developed with the linear equation A (H₂)/A (H₂O)=1.437(or 1.262)C×(H₂), where A (H₂)/A (H₂O) is the peak area ratio of H₂ and H₂O, and C (H₂) is the concentration of dissolved H₂ in mol/kg. The experimental temperature and pressure conditions did not influence the linear trend between the peak area ratio of A (H₂)/A (H₂O) and the concentrations of H₂, which indicated that the calibration model can be applied to high temperature and pressure environments.