ExoMol line lists -- LVI: The SO line list, MARVEL analysis of experimental transition data and refinement of the spectroscopic model

A semi-empirical IR/Vis line list, SOLIS, for the sulphur monoxide molecule $^{32}$S$^{16}$O is presented. SOLIS includes accurate empirical rovibrational energy levels, uncertainties, lifetimes, quantum number assignments, and transition probabilities in the form of Einstein $A$ coefficients covering the $X\,{}^{3}\Sigma^{-}$, $a\,{}^{1}\Delta^{ }$, $b\,{}^{1}\Sigma^{+}$, $A\,{}^{3}\Pi$, $B\,{}^{3}\Sigma^{-}$, $X\,{}^{\prime\prime3}\Sigma^{+}$, $A\,{}^{\prime 3}\Delta$ and $e\,{}^{1}\Pi$ systems and wavenumber range up to 43303.5 cm$^{-1}$ ($\geq 230.93$ nm) with $J\le 69$. SOLIS has been computed by solving the rovibronic Schr\"{o}dinger equation for diatomics using the general purpose variational code Duo and starting from a published ab initio spectroscopic model of SO (including potential energy curves, coupling curves, (transition) dipole moment curves) which is refined to experimental data. To this end, a database of 50106 experimental transitions, 48972 being non-redundant, has been compiled through the analysis of 29 experimental sources, and a self-consistent network of 8558 rovibronic energy levels for the $X$, $a$, $b$, $A$, $B$, and $C$ electronic states has been generated with the MARVEL algorithm covering rotational and vibrational quantum numbers $J \leq 69$ and $v \leq 30$ and energies up to 52350.40 cm$^{-1}$. No observed transitions connect to the $ B\,{}^{3}\Sigma^{-} (v = 0)$ state which is required to model perturbations correctly, so we leave fitting the $B\,{}^3\Sigma^-$ and $C\,{}^3\Pi$ state UV model to a future project. The SO line list is available at ExoMol from www.exomol.com.