Pressure dependence of peak positions, half widths, and peak intensities of methane Raman bands (ν2, 2ν4, ν1, ν3, and 2ν2)

Abstract

Results of investigation of changing peak positions, half widths, and peak intensities of Q‐branches of the ν2, 2ν4, ν1, ν3, and 2ν2 methane Raman bands are presented at pressures in the range 1–55 bar and а temperature of 298 K. The peak position of the ν2 band remains practically unchanged, and peak positions of all other bands, by analogy with the ν1 band, are shifted toward lower wavenumbers with pressure increase. It is demonstrated that the peak intensity ratio of any pair of the previously enumerated bands (except the pair of 2ν4 and 2ν2) is sensitive to pressure changes. When pressure increases, the decreased peak intensities of Q‐branches of depolarized ν2 and ν3 bands are caused by broadening of their rotational–vibrational lines, and the increased peak intensities of Q‐branches of the 2ν4 and 2ν2 bands are most likely caused by their increased interaction with the ν1 and ν3 bands. A set of data obtained will be useful for the Raman analysis of natural gas and can also be used for determination of the pressure of methane‐containing media. Copyright © 2017 John Wiley & Sons, Ltd.