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ExoMol project: Molecular line lists for exoplanet and other hot atmospheres

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The fundamental molecular data play principal role for spectral characterization of astrophysical objects cool enough to form molecules in their atmospheres (cool stars, extrosolar planets and planetary discs) as well as in a broad range terrestrial applications. The ExoMol project aims at providing comprehensive line lists for all molecules likely to be observable in exoplanet atmospheres in the foreseeable future (J. Tennyson and S. N. Yurchenko, MNRAS , 425, 21, 2012). The line lists for a number of key atmospheric species currently available from ExoMol ( [2]) are H2O , NH3, CaH, CaO, MgH, BeH, SiO, HCN /HNC, KCl, NaCl, CH4 , AlO, H2CO , ScH, PH3 , PN, HNO3 , SO2, SO3 and CS. Line lists currently under construction include those for AlH, C2, C3, SH, SiH, CrH, TiH, VO, H2S , and C2H4 .

For each line list the following components are required: (i) nuclear motion model, implemented in a computer program, for accurate calculations of rotation–vibration energies and wavefunctions; (ii) accurate potential energy and dipole moment functions and (iii) a computational procedure for intensity simulations based on the results of the nuclear motion calculations. The calculation of highly rotationally excited states (J up to 100) and, even more so, the calculation of huge lists of dipole transitions are computationally demanding in the extreme.

Special techniques are being developed to treat each case. For diatomic molecules we have developed a new program Duo, a flexible, multistate program capable of solving a general diatomic problem with arbitrary number and types of couplings. For small polyatomic molecules our main calculation tools are variational programs DVR3D and TROVE . For larger polyatomic molecules like C2H4 a combination of variational and perturbation theory approaches is used. In this talk I will discuss critical points of the large-scale production of molecular line lists involving high rotational excitations needed for simulating molecular spectra at temperatures higher than 500 K.

This talk is part of the Extra Theoretical Chemistry Seminars series.

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