| Résumé | Potential energy surfaces for all Born–Oppenheimer electronic states of IBr molecule correlating to the neutral 2P (2P3/2 and 2P1/2) iodine and bromine are calculated for the first time. Electric dipole and polarizability curves (static and transition) are also determined. Calculations include scalar and spin–orbit relativistic effects within all-electron Douglas-Kroll two-component Hamiltonian. Electron correlation is treated with quasi-degenerate multi-reference second-order perturbation theory. Seven adiabatic electronic states (X 1Σ+, A′ 3Π2, A 3Π1, 1 3Π0−, B 3Π0+, B′ 3Σ−0+, and 2 3Π0+) exhibit significant covalent bonding, and can support vibrational states. Calculated spectroscopic parameters agree with experiment to better than 1000 cm−1 (Te), 10 cm−1 (ωe), and 0.05 Å (re). A new 1 3Π0− state correlating to ground-state atoms is predicted at Te ≈ 14 000 cm−1, ωe ≈ 80 cm−1, and re ≈ 3.0 Å. The second new state (2 3Π0+) correlates to excited iodine atom, with Te ≈ 20 000 cm−1, ωe ≈ 115 cm−1, and re ≈ 3.3 Å. Non-adiabatic coupling parameters are calculated for the four avoided crossings, which arise due to electronic spin–orbit interaction. Estimated parameters of the B 3Π0+/B′ 3Σ−0+ crossing (Rc ≈ 3.32 Å; V ≈ 120 cm−1) agree with experimental values. The previously unsuspected 2 3Π0−/1 1Σ− crossing of two repulsive surfaces provides a new collisional deactivation channel for Br* atoms at relative velocities above 1000 m s−1. Several repulsive states (including 1 1Π1 and 2 3Π1) intersect the B/B′ system near the avoided crossing point, and may affect dynamics of IBr in strong laser fields. |
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