Extensive ab initio study of the electronic states of BSe radical including spin–orbit coupling

•The PECs of the 15 Λ–S states have been calculated for the first time.•The PECs of the 32 Ω states arising from 15 Λ-S states have been calculated.•The energy degeneracy among B2Σ + (II), C2Δ(I) and 2Σ−(I) states has been analyzed.•The double wells of C2Δ(I) ,2Σ−(I), 2Π(II) and 2Π(III) states have been studied.

The internally contracted multi-reference configuration interaction method (MRCI) with Davidson modification and the Douglas–Kroll scalar relativistic correction has been used to calculate the BSe molecule at the level of aug-cc-pV5Z basis set. The calculated electronic states, including 9 doublet and 6 quartet Λ-S states, are correlated to the dissociation limit of B(2Pu) + Se(3Pg) and B(2Pu) + Se(1Dg). The Spin-orbit coupling (SOC) interaction is taken into account via the state interaction approach with the full Breit-Pauli Hamiltonian operator, which causes the entire 15 Λ-S states to split into 32 Ω states. This is the first time that the spin-orbit coupling calculation has been carried out on BSe. The potential energy curves of the Λ-S and Ω electronic states are depicted with the aid of the avoided crossing rule between electronic states of the same symmetry. The spectroscopic constants of the bound Λ-S and Ω states were determined, which are in good agreement with the experimental data. The transition dipole moments (TDMs) and the Franck-Condon factors (FCs) of the transitions from the low-lying bound Ω states A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 to the ground state X2Σ+1/2 have also been presented. Based on the previous calculations, the radiative lifetimes of the A2Π(I)3/2, B2Π(I)1/2 and C2Δ(I)3/2 were evaluated.

Graphical abstractThe amplified view of the energy degeneracy of B2Σ+(II), C2Δ(I), 2Σ−(I), 2Δ(II) and 2Σ−(II) states.Figure optionsDownload full-size imageDownload as PowerPoint slide