Molecular Spectroscopy for Exoplanets
One can determine orbital radius, planetary size and planetary mass, and hence average density from techniques used to detect exoplanets. The only real means of expanding on this information is by spectroscopic study of atmospheres. To do this requires a knowledge of the spectroscopy of the molecules, present or likely to be present, in their atmosphere which in turn demands access to the extensive laboratory data that characterises these species. Given that the exoplanets whose spectra can be observed are largely hot compared to our planet, this puts particular demands on spectroscopic data needed both to interpret any observations and to perform radiative transport models of planets of interest. This chapter outlines the basic spectroscopy of atoms and molecules with a particular emphasis on the molecules that likely to form in exoplanetary atmospheres. The importance of treating the temperature dependence of the spectrum and the huge growth in the number of lines which play a role at higher temperatures, such as those deduced for hot Jupiter exoplanets, is emphasized. Sources of data for use in studies of exoplanets are discussed in detail and illustrative examples given.
I thank the members of the ExoMol team for their contribution to the work reported here; in particular I would like to thank Sergey Yurchenko both for his contribution to the project and his help with preparing some of the figures shown here. I also thank Phillip Coles and Clara Sousa-Silva for supplying figures, and Tony Lynas-Gray for many helpful comments on the original manuscript.
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