Molecular dynamics simulations of pressure-broadened symmetric-top gas spectra. Application to CH₃F-Ar and CH₃F-He mixtures

We present a new approach, based on requantized classical molecular dynamics simulations (rCMDS), to calculate pressure-broadened absorption spectra of symmetric-top molecules. We test it in the cases of CH₃F-He and CH₃F-Ar gas mixtures at room temperature for which predictions are made, without use of any adjusted parameter, based on input inter-molecular potentials from the literature. The results show that the Lorentz pressure-broadenings, deduced from fits of the computed spectra, are in good agreement with available measured values. Furthermore, the predicted effects of line-mixing at high pressure are also very consistent with observations. In addition, the study of the influence of the speed dependence of the pressure-broadening coefficient is promising but needs to be confirmed, since based on only one experimental result available. This opens renewed perspectives for predictions of symmetric-top molecules line shapes beyond the Voigt profile.