Self and N2 collisional broadening of far-infrared methane lines measured at the SOLEIL synchrotron

Following our recent study devoted to measurements of intensities of pure rotation lines of methane, room temperature far infrared spectra of methane diluted in nitrogen at five total pressures between 100 and 800 hPa have been recorded at the AILES beamline of the SOLEIL synchrotron. One hundred and five N2 broadening coefficients of methane pure rotation lines have been measured in the 83-261 cm−1 spectral range using multi-spectrum non-linear least squares fitting of Voigt profiles. Pressure-induced line shifts were not needed to fit the spectra to the noise level and line mixing effects were neglected. One hundred and seventy-six self broadening coefficients have also been measured in the 59-288 cm−1 spectral range using the pure methane spectra recorded in our previous work. The measured N2 broadening coefficients were compared to semi-classical calculations.

► Self and N2 broadening coefficients measured for pure rotation lines of 12CH4. ► Spectra recorded at the AILES beamline of the SOLEIL synchrotron. ► First measurements of broadening coefficients in the THz spectrum of methane. ► N2 broadening coefficients calculated using a modified Robert-Bonamy formalism.