Infrared spectra of trifluoromethane isotopologues ( 12 CHF3 , 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. 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 1 CDF3, composed of 89662832, 33068581 and 23265983 lines, respectively. The final theoretical spectrum of CHF 3 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.