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

- 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.

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.