Experimental determination of the Raman CH4 symmetric stretching (ν1) band position from 1–650 bar and 0.3–22 °C: Application to fluid inclusion studies

The position of the Raman methane (CH4) symmetric stretching band (ν1) over the range 1–650 bar and 0.3–22 °C has been determined using a high-pressure optical cell mounted on a Raman microprobe. Two neon emission lines that closely bracket the CH4 band were collected simultaneously with each CH4 spectrum. The peak position was determined after least squares fitting using a summed Gaussian–Lorentzian method, resulting in a precision of ≈±0.02 cm−1 in peak position determination. The CH4ν1 band position shifts to lower wave number with increasing pressure. At a given pressure, the band shifts to lower wave number with decreasing temperature, and the magnitude of the temperature shift increases with increasing pressure. The relationship between the Raman CH4ν1 band position and temperature and pressure determined here may be used to estimate the internal pressure in natural or synthetic CH4-bearing fluid inclusions. This information, in turn, may be used to determine the density of pure CH4 fluid inclusions and the salinity of CH4-bearing aqueous inclusions.