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^⋆

¹ Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 7331, BP 1039, 51687 Reims Cedex 2, France
e-mail: michael.rey@univ-reims.fr
² Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA, CNRS UMR 7583), Université Paris Est Créteil, Université Paris Diderot, Institut Pierre-Simon Laplace, 94010 Créteil, France
³ Laboratory of Theoretical Spectroscopy, Institute of Atmospheric Optics, SB RAS, 634055 Tomsk, Russia
⁴ Laboratory of Quantum Mechanics of Molecules and Radiative Processes, Tomsk State University, 36 Lenin Avenue, 634050 Tomsk, Russia

Received: 26 May 2016
Accepted: 8 July 2016

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.