Experimental determination of the Raman CH 4 symmetric stretching ( ν1) band position from 1–650 bar and 0.3–22 °C: Application to fluid inclusion studies

Abstract

The position of the Raman methane (CH 4) symmetric stretching band ( ν 1) 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 CH 4 band were collected simultaneously with each CH 4 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 CH 4 ν 1 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 CH 4 ν 1 band position and temperature and pressure determined here may be used to estimate the internal pressure in natural or synthetic CH 4-bearing fluid inclusions. This information, in turn, may be used to determine the density of pure CH 4 fluid inclusions and the salinity of CH 4-bearing aqueous inclusions.