Methyl bromide spectral lines broadening by collision with N2

Abstract

In this study, we investigated the broadening of methyl bromide (CH₃Br) rotational lines induced by collision with nitrogen (N₂), using a newly developed ab initio multi-dimensional potential energy surface (PES) for the CH₃Br–N₂ van der Waals complex. The radial coefficients of the PES were optimized through a least-squares fitting procedure and then adjusted using fractional functions to enable integration into our collisional broadening computation code. Then, we applied the semi-classical Modified Robert and Bonamy (MRB) model, enhanced by the exact trajectory approach, to calculate the N₂-induced broadening coefficients for CH₃Br ro-vibrational lines at room temperature. Results are provided for various branches of the parallel ν₂ vibrational band of CH₃Br. Our results are roughly consistent with the available experimental data, but through this work, we aim to highlight the weaknesses of the MRB model. Our findings are useful for more understanding and clearer delineation of the limitations of the MRB model.