An Exomol Line List For So: Rovibronic Spectrum Of Sulfur Monoxide

The work we present here is a diatomic molecule line list study on the molecule sulfur monoxide (SO), suitable for characterising exoplanetary atmospheres up to temperatures of 4000 K. The motivation of this project is to provide comprehensive line list data applicable to modelling high temperature spectra in environments such as e.g. exoplanetary atmospheres, where current spectroscopic databases provide only limited coverage. The new SO line list will be included into the ExoMol database.\footnote{J.~Tennyson et al. \emph{J. Quant. Spectrosc. Radiat. Transf.}, 2020, \textbf{255}, 107228; \textit{www.exomol.com}.} A production of such a line list first includes the creation of a MARVEL\footnote{T.~Furtenbacher, A.~G. Cs\'asz\'ar, J.~Tennyson, {MARVEL: measured active rotational-vibrational energy levels}, J. Mol. Spectrosc. 245 (2007) 115--125.} set of rovibroic energies, calculation of high-level \textit{ab initio} potential energy curves (PECs), spin-orbit curves (SOCs), electronic-angular momentum curves (EAMCs) and transition moment dipole curves (TDMCs) using \textsc{MOLPRO} %\footnote{H.-J. Werner, P.~J. Knowles, G.~Knizia, F.~R. Manby, M.~Sch\"utz, \emph{WIREs Comput. Mol. Sci.}, 2012, \textbf{2}, 242--253.} at MRCI level of theory and a solution of coupled ro-vibronic Schr\"{o}dinger equations using the variational code \textsc{Duo}\footnote{S.~N. Yurchenko, L.~Lodi, J.~Tennyson, A.~V. Stolyarov, \emph{Comput. Phys. Commun.}, 2016, \textbf{202}, 262 -- 275; publicly available at \textit{https://github.com/Trovemaster/Duo}.}. The PECs, SOCs and EAMCs are represented by analytical parametrised functional forms and refined by fitting to the MARVEL energies. A rovibronic line list for SO consists of energies, frequencies, Einstein coefficients and a partition function covering all electronic states up to 50\,000~cm$^{-1}$, including $X$~$^3\Sigma^-$, $A$~$^3\Pi$, $A'$~$^3\Delta$, $A''$~$^3\Sigma^+$, $B$~$^3\Sigma^-$, $C$~$^3\Pi$, $a$~$^1\Delta$, $b$~$^1\Sigma^+$ and $c$~$^1\Sigma^-$. IR/Vis/UV absorption and emission spectra of SO for a set of temperatures are generated using the program ExoCross.\footnote{S.~N. {Yurchenko}, A.~F. {Al-Refaie}, J.~{Tennyson}, \emph{Astron. Astrophys};, 2018, \textbf{614}, A131; publicly available at \textit{https://github.com/Trovemaster/ExoCross}.