2025MNRAS.538.2693M

In this work, the R-matrix method was employed to calculate the total and partial-channel photoionization cross-sections for the initial three bands of hydrogen sulfide ($\mathrm{H_2S}$), four bands of carbon disulfide ($\mathrm{CS_2}$), and three bands of carbonyl sulfide ($\mathrm{OCS}$) molecules. These calculations were performed over the entire range of photon energy, starting from the ionization thresholds of the respective states and extending significantly beyond the final level thresholds of the target ions. The present computations are performed within the fixed-nuclei approximation, which does not consider vibration or rotation. However, it incorporates electron correlation effects and resonant photoionization contributions that have not been considered in any previously published literature. Intense absorption is observed in the total photoionization cross-section at energies below 20 eV, with a significant portion of it being caused by the excitation of molecules that subsequently decay by strong autoionization. These are assigned to Rydberg levels strengthened by the remarkably extensive partial photoionization of the $\left(2 b_1^{-1}\right) \mathrm{X}^2 \mathrm{B_1}$ channel in $\mathrm{H_2S}$, $\left(2 \pi _g^{-1}\right) \mathrm{X}^2 \mathrm{\Pi _g}$ channel in $\mathrm{CS_2}$, and $\left(3 \pi ^{-1}\right) \mathrm{X}^2 \mathrm{\Pi }$ channel in $\mathrm{OCS}$, within the 10-16 eV excitation range. The current R-matrix results are mostly in line with previous experimental measurements and theoretical calculations. There are some differences, though, which can be explained by the large number of Rydberg resonances just above the photoionization threshold. The computed data are crucial for modelling parameters observed in photoionized plasmas.