A theoretical study of the low-lying electronic states of OIO and the ground states of IOO and OIO⁻

Abstract

Several low-lying electronic states of OIO were investigated at the multireference configuration interaction (MRCI) level of theory. The state, which is the origin of the absorption bands observed experimentally, is calculated to be bound with respect to dissociation to IO + O. A low barrier for dissociation to I + O₂ is calculated for the state, which should lead to efficient I atom production. This indirect process would involve an initial spin–orbit interaction between the state and the nearby B²A₁, followed by a strong vibronic interaction with the A²B₂ state via an avoided crossing. Accurate near-equilibrium potential energy functions have also been determined for OIO, IOO, and OIO⁻ using sequences of correlation consistent basis sets extrapolated to the complete basis set limit using MRCI or coupled cluster methods. These were then used to calculate rotational and vibrational spectroscopic constants. Accurate bond dissociation energies and enthalpies of formation have also been calculated. The use of additional tight functions in the iodine basis sets were found to be essential for both accurate energetics and structures, and in particular their use leads to a revision of a previously calculated dissociation energy of IO that is now also in near perfect agreement with experiment.

Keywords:

• iodine dioxide
• electronic states
• thermochemistry
• potential energy functions
• photodissociation

Acknowledgements

The support of the National Science Foundation (CHE-0723997) is gratefully acknowledged.