2024MNRAS.528.3823G

The sulfur dimer (S₂) 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 ultraviolet (UV) spectrum of S₂ contains transitions between vibronic levels above and below the dissociation limit, giving rise to a distinctive spectral signature. Using spectroscopic information from the literature, and the spectral simulation program PGOPHER, a UV line list of S₂ 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'≥10 are pre-dissociated. Intensities have been calculated from existing experimental and theoretical oscillator strengths, and semi-empirical strengths for the pre-dissociated bands of S₂ have been derived from comparisons with experimental cross-sections. The S₂ line list also includes the $B^{\prime \prime }\, ^{3}\Pi _{u}-X\, ^{3}\Sigma ^{-}_{g}$ (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 S₂ line list and its validation against existing laboratory spectra. The extensive line list covers the spectral range 21 700-41 300 cm^–1 (∼242-461 nm) and can be used for modelling both absorption and emission.