Infrared spectra of trifluoromethane isotopologues (12CHF3, 13CHF3, and 12CDF3) from high-accuracy ab initio calculations for atmospheric analysis of hydrofluorocarbons

Abstract

Trifluoromethane (CHF₃) is a pollutant gas with a large global warming potential. Although CHF₃ emissions are actively monitored using ground- and space-based spectrometers, this molecule is still absent from the reference spectroscopic databases. CHF₃ exhibits complex resonance interactions among its ro-vibrational energy levels, resulting in a highly congested infrared spectrum with irregular patterns. To support atmospheric retrieval procedures for CHF₃, accurate spectral predictions are thus required, particularly for line intensities. We present the first global prediction of the ro-vibrational spectrum of CHF₃ using an effective model based on full-dimensional ab initio potential energy and dipole moment surfaces. The non-empirical effective model presented here can be considered as an efficient alternative to full variational calculations for polyatomic molecules. This model includes the most relevant cold and hot transitions at room temperature in the region of the fundamental bands (0–3100 cm⁻¹). To this end, 670 vibrational sub-states corresponding to a polyad number of P_max = 22 (≈ 4500 cm⁻¹) were considered, together with rotational angular momentum values up to J_max = 99, leading to the construction of comprehensive line lists for ¹²CHF₃, ¹³CHF₃, and ¹²CDF₃, composed of 89662832, 33068581 and 23265983 lines, respectively. The final theoretical spectrum of CHF₃ was successfully validated against cross sections measured by the Pacific Northwest National Laboratory. This work clearly demonstrates the advantages of ab initio calculations for predicting ro-vibrational spectra of heavy polyatomic molecules, such as those containing F, Cl or Br.