Electronic spectrum of ${\mathrm{S}}_2^{\mathrm{-}}$, the electron affinity of ${\mathrm{S}}_2$, and the binding energies of neutral and anionic ${\mathrm{S}}_3$ clusters

The low-lying electronic states of the ${\mathrm{S}}_2^{\mathrm{-}}$ anion have been investigated by quantum-chemical methods incorporating an extensive treatment of electron correlation. All excited doublet states that can be reached in spin- and dipole-allowed transitions from the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ ground state of the anionic disulfur molecule as well as the lowest quartet state ${}_{}{}^4{}_{}{}^{}\mathrm{\Sigma }_{\mathit{u}}^{\mathrm{-}}{}_{}{}^{}$ are characterized by their spectroscopic constants, excitation energies, and transition dipole matrix elements with the ground state. Furthermore, an accurate calibration of the employed theoretical methods with respect to the electron affinity of the sulfur atom, the potential energy curves for the ground states of ${\mathrm{S}}_2$ and ${\mathrm{S}}_2^{\mathrm{-}}$, the electron affinity of ${\mathrm{S}}_2$, and the binding energies of the neutral and anionic ${\mathrm{S}}_3$ clusters is presented.