Study of collisional broadening and beyond-Voigt parameters of v₄ methane lines broadened by helium using a high-resolution dual-comb spectrometer

In this work, the line-shape parameters of methane lines broadened by helium in the ν₄ vibrational band were determined at room temperature. Experimental spectra with 7 total pressures ranging from 26 to 536 mbar were recorded using a high-resolution dual-comb spectrometer based on quantum cascade lasers. Recent improvements to this instrument have resulted in high quality spectra and fast measurements. The Voigt, Nelkin-Ghatak, speed-dependent Voigt and speed-dependent Nelkin-Ghatak theoretical line profiles were adjusted to the experimental methane line-shapes to determine the spectroscopic parameters. The first-order line-mixing effect was included using Rosenkranz’s approximation in addition to each theoretical model. To our knowledge, line-shape parameters were determined for the first time for multiple ν₄ band CH₄ lines diluted in He. A very good agreement was found with the available literature.