Methane-induced pressure effects on the CO and OH Raman bands in methanol vapor.

Methanol is widely employed in natural gas extraction as a hydrate inhibitor, making accurate monitoring of its concentration critical for ensuring safety and process efficiency. Raman spectroscopy is a promising tool for real-time, in situ analysis of natural gas composition. However, high-accuracy measurements require accounting for the effects of thermodynamic conditions on the vibrational bands of the constituent species. In this work, the influence of methane on the Raman bands associated with the CO and OH stretching vibrations of methanol in the gas phase is investigated for the first time. The positions, widths, and asymmetry coefficients of the methanol Q-branches were measured over a pressure range of 1-30 bar. We propose a method to simulate the effect of methane on the Raman spectrum of methanol using a methanol/argon mixture. This approach significantly reduces the measurement error to below 1-2 % across the studied pressure range. These results are useful both for developing high-accuracy Raman-based gas analysis techniques and for validating quantum-chemical models of intermolecular interactions.