A HITRAN-formatted UV line list of S$_2$ containing transitions involving $X\,^{3}\Sigma^{-}_{g}$, $B\,^{3}\Sigma^{-}_{u}$, and $B''\,^{3}\Pi_{u}$ electronic states

Abstract

The sulfur dimer (S$_2$) is an important molecular constituent in cometary atmospheres and volcanic plumes on Jupiter's moon Io. It is also expected to play an important role in the photochemistry of exoplanets. The UV spectrum of S$_2$ contains transitions between vibronic levels above and below the dissociation limit, giving rise to a distinctive spectral signature. By using spectroscopic information from the literature, and the spectral simulation program PGOPHER, a UV line list of S$_2$ is provided. This line list includes the primary $B\,^{3}\Sigma^{-}_{u}-X\,^{3}\Sigma^{-}_{g}$ ($v'$=0-27, $v''$=0-10) electronic transition, where vibrational bands with $v'$$\geq$10 are predissociated. Intensities have been calculated from existing experimental and theoretical oscillator strengths, and semi-empirical strengths for the predissociated bands of S$_2$ have been derived from comparisons with experimental cross-sections. The S$_2$ line list also includes the $B''\,^{3}\Pi_{u}-X\,^{3}\Sigma^{-}_{g}$ ($v'$=0-19, $v''$=0-10) vibronic bands due to the strong interaction with the $B$ state. In summary, we present the new HITRAN-formatted S$_2$ line list and its validation against existing laboratory spectra. The extensive line list covers the spectral range 21700$-$41300~cm$^{-1}$ ($\sim$242$-$461~nm) and can be used for modeling both absorption and emission.