ИСТИНА

Collision-induced absorption (CIA) in the millimeter and far-infrared ranges contributes appreciably to the total absorption of radiation in planetary atmospheres. To aid atmospheric and planetary scientists reference spectroscopic data for CIA are provided in the dedicated section [1] of the HITRAN database [2]. Titan’s atmosphere is composed mainly of nitrogen, with a small percentage of methane and hydrogen. Collision-induced absorption by molecular complexes involving N2 and CH4 contributes to a greenhouse effect in the Titan’s atmosphere. The uncertainty of the CH4-N2 CIA in the far-infrared may have a severe impact on retrieval of the height profiles of minor atmospheric constituents. Recent opacity models utilized the semiempirical model [3] for the CH4-N2 CIA adjusted to existing experimental data. In [4], the correctness of models [3] is questioned, and a heuristic correction factor is adopted to fit limb-scan data. The trajectory-based approach proved itself [5] to be a practical alternative to both quantum mechanical [6] and classical many-body [7] perspectives in the modeling of CIA band profiles. Note that up-to-now a fairly limited number of molecular pairs have been studied without recourse to the use of adjustable parameters. In this work, we extend the trajectory-based non-empirical approach to model CIA band profiles of methane-containing molecular pairs. Our approach relies on the use of high-level quantum-chemically characterized potential energy and induced dipole surfaces. Classically exact equations of motion for colliding molecules are solved from a thermal distribution of initial conditions. The spectral profile is calculated as an averaged Fourier spectrum of the induced dipole moment. We discuss the reliability of our calculated CIA profiles in light of their comparison with existing experimental and semiempirical data. This work is partially supported by RFBR Grant 18-05-00119, Program 12 by Presidium of RAS and NASA HITRAN grant. 1. Karman, et al. (2019). Icarus. 328, 160. 2. Gordon, et al. (2017). JQSRT. 203, 3. 3. Borysow, et al. (1993). Icarus. 105, 175. 4. Anderson, et al. (2010). Icarus. 212, 762. 5. Chistikov, et al. (2019). J. Chem. Phys. 151, 194106. 6. Karman, et al. (2015). J. Chem. Phys. 142, 084306. 7. Bussery-Honvault, et al. (2014). J. Chem. Phys. 140, 054309.