Pressure broadening in Raman spectra of CH4-N2, CH4-CO2, and CH4-C2H6 gas mixtures

Aleksandr S Tanichev; Dmitry V Petrov

doi:10.1016/j.saa.2023.122396

Pressure broadening in Raman spectra of CH₄-N₂, CH₄-CO₂, and CH₄-C₂H₆ gas mixtures

Spectrochim Acta A Mol Biomol Spectrosc. 2023 Apr 15:291:122396. doi: 10.1016/j.saa.2023.122396. Epub 2023 Jan 20.

Authors

Aleksandr S Tanichev¹, Dmitry V Petrov²

Affiliations

¹ Laboratory of Ecological Instrumentation, Institute of Monitoring of Climatic and Ecological Systems, 634055 Tomsk, Russia. Electronic address: tanichev_aleksandr@mail.ru.
² Laboratory of Ecological Instrumentation, Institute of Monitoring of Climatic and Ecological Systems, 634055 Tomsk, Russia; Department of Optics and Spectroscopy, Tomsk State University, 634050 Tomsk, Russia.

PMID: 36696859
DOI: 10.1016/j.saa.2023.122396

Abstract

Different molecular environments change the spectrum of a given gas sample involved in a mixture compared to the spectrum of a pure gas. It is necessary to account for this effect to improve the accuracy of the analysis of the natural gas composition by Raman spectroscopy. First, the change in the main components of natural gas (methane, nitrogen, carbon dioxide, and ethane) must be considered. This work is devoted to the mutual influence of CH₄-N₂, CH₄-CO₂, and CH₄-C₂H₆ on their characteristic Raman bands in the range of 300-2500 cm^-1. The half-width and asymmetry of the Q branches of N₂, CO₂, and C₂H₆ as a function of methane concentration were obtained in the range of 1-50 bar. The averaged broadening coefficients of the rotational-vibrational lines of the ν₂ band of CH₄ perturbed by N₂, CO₂, and C₂H₆ are measured. A high-sensitivity spectrometer with a resolution of 0.5 cm^-1 based on spontaneous Raman scattering was used to obtain reliable results. The algorithm and all the necessary parameters for simulating the effect of various molecular environments on the Raman bands of the main components of natural gas are presented.

Keywords: Gas mixtures; Methane; Natural gas; Pressure broadening; Raman spectroscopy.