Theoretical study of collision and collision-free radiative lifetimes of ${{\text{S}}_2}\left( {{{\text{B}}^3}\Sigma_{\text{u}}^{-} \left( {{\upsilon^{\prime}} = 0 - 9} \right)} \right)$

Abstract

We calculate multireference configuration-interaction wavefunctions and the potential-energy curves for the ${B^3}\Sigma_u^{-}$ and ${X^3}\Sigma_g^{-}$ states of the collision-free S₂ molecule and the T-shape collision complex S₂–He using cc-pVQZ basis sets. We obtain the transition dipole moments of the ${{\text{S}}_2}\left( {{B^3}\Sigma_u^{-} \to {X^3}\Sigma_g^{-} } \right)$ and the Franck–Condon factors between the vibrational levels of this two states. We evaluate the radiative lifetimes of ${{\text{S}}_2}\left( {{B^3}\Sigma_u^{-} \left( {{\upsilon^{\prime}} = 0 - 9} \right)} \right)$ levels of the collision complex and the collision-free molecule and compare them with the experiments. The collision provides little change in the radiative lifetimes of ${{\text{S}}_2}\left( {{B^3}\Sigma_u^{-} \left( {{\upsilon^{\prime}} = 0 - 9} \right)} \right)$ according to the previous calculations. We obtain excellent agreement between the theoretical results and the experiments. The data calculated are very useful in the study of the microwave-driven high-pressure sulfur lamp and an S₂ laser pumped by a transverse fast discharge.