Extensive investigation on spectroscopic properties and predissociation mechanisms of the Se2+ cation

Spectroscopic properties of the ${\text{Se}}_2^{+}$ cation are studied using high-level ab initio methods. Scalar relativistic (SR) corrections, core-valence (CV) electron correlation and spin-orbit coupling (SOC) effects are taken into account. The potential energy curves (PECs) of 19 Λ-S states and 52 Ω states generated from the Λ-S coupling scheme are obtained at the multireference configuration interaction plus Davidson correction (MRCI + Q) level of theory. The spectroscopic constants of bound states have been calculated, showing good agreement with previous experimental Se₂ photoionization results. Various curve crossings involving the $b^4{\Sigma }_g^{-}$ and $B^2{\Sigma }_g^{-}$ states of ${\text{Se}}_2^{+}$ are revealed and their predissociation mechanisms are predicted. Finally, the electric dipole transition moments and Franck-Condon factors of the $b^4{\Sigma }_g^{-}-a^4{\Pi }_u$, $B^2{\Sigma }_g^{-}-A^2{\Pi }_u$, $C^2{\Sigma }_u^{+}-X^2{\Pi }_g$, and $A^2{\Pi }_u-X^2{\Pi }_g$ transitions are obtained and augmented by estimations of the radiative lifetimes of the photo-stable excited $b^4{\Sigma }_g^{-}$, $B^2{\Sigma }_g^{-}$, $C^2{\Sigma }_u^{+}$, and $A^2{\Pi }_u$ states. We believe that our research can provide a basis for further experimental studies of the ${\text{Se}}_2^{+}$ cation including predictions of its luminescence which also may be of astrophysical interest since selenium already has been detected in space.