Molecule opacities of X²Σ⁺, A²Π, and B²Σ⁺ states of CS⁺

Carbon sulfide cation (CS⁺) plays a dominant role in some astrophysical atmosphere environments. In this work, the rovibrational transition lines are computed for the lowest three electronic states, in which the internally contracted multireference configuration interaction approach (MRCI) with Davison size-extensivity correction (+Q) is employed to calculate the potential curves and dipole moments, and then the vibrational energies and spectroscopic constants are extracted. The Frank-Condon factors are calculated for the bands of X²Σ⁺-A²Π and X²Σ⁺-B²Σ⁺ systems, and the band of X²Σ⁺-A²Π is in good agreement with the available experimental results. Transition dipole moments and the radiative lifetimes of the low-lying three states are evaluated. The opacities of the CS⁺ molecule are computed at different temperatures under the pressure of 100 atms. It is found that as temperature increases, the band systems associated with different transitions for the three states become dim because of the increased population on the vibrational states and excited electronic states at high temperature.