Extensive theoretical studies on the low-lying electronic states of BBr⁺

The potential energy curves (PECs) of two lowest dissociation channels of BBr(+) have been thoroughly investigated using the internally contracted multireference configuration interaction method with Davidson correction and relativistic correction. All PECs are extrapolated to complete basis set limit. Several quasibound excited states caused by avoided crossings are found. Based on the PECs, the spectroscopic parameters of bound and quasibound states are obtained. The transition dipole moments and radiative lifetimes are predicted for all possible transitions. Finally, the spin-orbit coupling matrix elements are computed using the states interaction approach with the full Breit-Pauli Hamiltonian to analyze the interactions in PECs crossing regions. We propose that the 2(2)Σ(+)-X(2)Σ(+) and 2(2)Π-X(2)Σ(+) transitions which cannot be observed in experiments are attributed to the intricate couplings among 1(2)Π, 2(2)Π, 2(2)Σ(+), 1(4)Σ(+), 1(4)Δ, 1(4)Σ(-), 1(2)Δ and 1(2)Σ(-) states.