Spin−Orbit Configuration Interaction Calculation of the Potential Energy Curves of Iodine Oxide

An ab initio configuration interaction (CI) study including spin−orbit coupling is carried out for the ground and excited states of the IO radical by employing relativistic effective core potentials. The computed spectroscopic constants are in good agreement with available experimental data, with some tendency to underestimate the strength of bonding. The first excited state, a4Σ-, which has not yet been observed experimentally, is predicted to be bound by 30.1 kJ/mol and to have a significantly larger equilibrium distance than the ground state. It is split by spin−orbit interaction into 1/2 and 3/2 components, with the 1/2 component being the lower one with a calculated spin−orbit splitting of 210 cm-1. The most interesting state in the low-energy IO spectrum, A12Π3/2, is shown to be predissociated due to interaction with a number of repulsive electronic states. Predissociation of the A1, v‘ = 0, 1 vibrational levels is attributed to a fairly weak spin−orbit coupling with the 2Δ3/2 state, while rotationa...