Formation of S2 species in different redox states by radiative association in atomic and ionic collisions

Abstract

Radiative associations for formations of the S₂, S₂⁺ and S₂^- molecular species during atomic collisions S(³P_u) + S(³P_u), S(³P_u) + S⁺(⁴S_u) and S(³P_u) + S^-(²P_u) are investigated. The adiabatic potential energy curves (PECs) and spin-allowed transition dipole moments (TDMs) are obtained by the internally contracted multireference configuration interaction method with the Davidson correction (icMRCI+Q). A number of PECs and TDMs are chosen to calculate the corresponding cross-sections and rate coefficients of radiative associations. The calculated rate coefficients are valid for the temperatures from 100 to 16000 K and fitted to the analytical function according to the three-parameter Arrhenius–Kooij formula. These results indicate that transitions originating in the ΔΛ=0 selection rule are the main contributors for the radiative association process. The present study can elucidate the further understanding the radiative association, which plays an important role in the formation and evolution of the S₂, S₂⁺ and S₂^- molecules.