2025A&A...699A.264W

Addressing the formation for MgS, a relevant astrophysical problem for carbon rich stars, we have employed quantum mechanical ab initio calculations to predict the radiative association cross section and association rate coefficient of magnesium and sulfur atoms forming the magnesium sulfide molecule. This was accomplished by accounting for the emissive 1¹Π → X¹Σ⁺, 1¹Δ → 1¹Π, and 1³Σ^– →a³Π transitions that make significant contributions to the radiative association process. The atomic ground state, Mg(¹S), and the metastable excited state, S(¹D), represent the lowest singlet dissociation limit common for the studied radiative association channels, whereas the ground states Mg(¹S) and S(³P) represent the lowest triplet dissociation limit for these channels. The computational results show that in the temperature range of 10-10 000 K, the 1¹Π → X¹Σ⁺ transition dominates the formation of MgS through radiative association in the collision of Mg(¹S) and S(¹D) atoms, while the 1¹Δ → 1¹Π transition plays an important role at higher temperatures. The total rate coefficient for the singlet-singlet transitions ranges from 3.78 × 10^–18 cm³ s^–1 to 4.79 × 10^–17 cm³ s^–1, while that for the triplet-triplet transition ranges from 2.02 × 10^–22 cm³ s^–1 to 6.79 × 10^–18 cm³ s^–1. These total rate coefficients were fit using the three-parameter fit Arrhenius-Kooij function, which is expected to be helpful for the celestial modeling.