First theoretical global line lists of ethylene (¹²C₂H₄) spectra for the temperature range 50−700 K in the far-infrared for quantification of absorption and emission in planetary atmospheres

Abstract

We present the construction of complete and comprehensive ethylene line lists for the temperatures 50−700 K based on accurate ab initio potential and dipole moment surfaces and extensive first-principle calculations. Three lists spanning the [0−6400] cm −1 infrared region were built at T = 80, 160, and 296 K, and two lists in the range [0−5200] cm −1 were built at 500 and 700 K. For each of these five temperatures, we considered possible convergence problems to ensure reliable opacity calculations. Our final list at 700 K was computed up to J = 71 and contains almost 60 million lines for intensities I > 5 × 10 −27 cm/molecule. Comparisons with experimental spectra carried out in this study showed that for the most active infrared bands, the accuracy of band centers in our theoretical lists is better on average than 0.3 cm −1 , and the integrated absorbance errors in the intervals relevant for spectral analyses are about 1−3%. These lists can be applied to simulations of absorption and emission spectra, radiative and non-LTE processes, and opacity calculations for planetary and astrophysical applications.

Total internal partition sums for the HITRAN2020 database

“…The rotational constants are from Tan et al [106] and [107], respectively, and for Qrot with the constants of Herbin et al [111] and Qvib calculated using the HOA with the vibrational constants of Viglaska et al [112]. The 296 K partition sums calculated in this work are in a good agreement with the ab initio direct sum results of Rey et al [113] for 12 C2H4 , the difference being of 0.4% .…”

The ExoMol Atlas of Molecular Opacities

“…Although not shown here, the main features of the ethylene spectrum show an unusually small sensitivity to temperature [75]. Rey et al [108] have also computed a far-infrared ethylene line list. Figure 3 shows cross sections for a variety of polyatomic oxides plus hydrogen cyanide.…”

A global view of isotopic effects on ro-vibrational spectra of six-atomic molecules: a case study of eleven ethylene species

“…The most extended theoretical spectra predictions for the main ethylene isotopologue 12 C 2 H 4 using molecular PES 30 and DMS 31 have been published in Ref. 32 (see also Ref. 33 as part of the Exomol project) and included in the TheoReTS information system 29 .…”