Abstract
In this work, we measured the intensities of Q-branches of the ν1, ν2 and ν3 bands in the polarized and depolarized methane Raman spectra in the pressure range of 1–60 atm. It was established that the pressure dependence of depolarization ratios of the ν2 and ν3 bands are negligible. In turn, the depolarization ratio of the ν1 band increases with increasing pressure and reaches approximately 0.0045 at 60 atm. These data are more precise than previously published ones because ν1 band intensities were determined taking into account the contribution of overlapping lines of ν3 band. The presented data will be useful in calculating the methane polarizabilities at high pressure, as well as in calculating methane Raman spectra for measuring the natural gas composition using Raman spectroscopy.
Highlights
Methane is one of the most abundant molecules on Earth
The performed studies showed that the dependence of depolarization ratios of the ν2 and ν3 bands on pressure is negligible
The degree of depolarization of the ν1 band increases with pressure and reaches approximately 0.0045 at 60 atm. These data are significantly lower than those published earlier. This is explained by the fact that in our work we used an experimental setup with higher sensitivity, and took into account the contribution of the lines of the ν3 band located in the region of 2916–2917 cm−1
Summary
Methane is one of the most abundant molecules on Earth. It is present in atmospheric air, often found in inclusions in minerals, and is the dominant component of natural gas. One of the important characteristics of the Raman bands, along with the position, half-width, and scattering cross-section, is the depolarization ratio (ρ). This value characterizes the symmetry of the vibrations and is defined as the ratio I⊥ /Ik , where I⊥ and Ik are the
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