Configuration interaction investigation including spin–orbit coupling effect for electronic states of IBr and its cation

Iodine monobromide (IBr) and its cation (IBr+), which play an important role in the stratospheric ozone depletion, have received much attention. However, the electronic states of IBr/IBr+ have not been well understood. In this paper, the potential energy curves (PECs) of low-lying electronic states for IBr/IBr+ were computed with high-level multireference configuration interaction (MRCI) method. The spin–orbit coupling effect was taken into account via the state interaction method with the full Breit–Pauli Hamiltonian. For IBr, the PECs of 12 Λ–S states correlated with the lowest dissociation limit of IBr molecule and 23Ω states generated from those Λ–S states were calculated. The spectroscopic constants of the bound states were obtained, which are consistent with previous experimental results. The two avoided crossing points between (2)0+/(3)0+ and (3)0+/(4)0+ were interpreted by analysis of Λ–S compositions of Ω states at various bond lengths. Based on potential energy curves and transition dipole moments, the radiative lifetime of 13Π1 was evaluated. For IBr+, the PECs of 12 Λ–S states and 4 low-lying Ω states were calculated, from which the spectroscopic constants were evaluated. Finally, the ionization energies from the neutral ground state (X1Σ+) to different ionic states (X2Π3/2, X2Π1/2, A2Π3/2 and A2Π1/2) were obtained. •The potential energy curves of IBr and IBr+ were calculated with configuration interaction method including spin–orbit coupling effect.•Spectroscopic parameters for bound states of IBr and IBr+ were computed.•The radiative lifetime of 13Π1 state of IBr was evaluated.•The ionization energies of IBr were given.