Ab initio potential functions for the ionic states of OH

Potential curves of the OH molecule correlating to the four lowest energy dissociation limits O(3P)+H(2S), O(1D)+H(2S), O(1S) + H(2S), O−(2P) + H+ have been computed at the CI/CASSCF level with the AUG-cc-pVTZ basis sets with a special emphasis on the ion-pair states 3 2Π and C 2Σ+. A balanced treatment of the excited state potentials is achieved by using the state-averaging MO optimization procedure. The X 1Σ+ and 1Π potentials of OH− have been also considered. After empirical correction of the errors at the dissociation limits, the computed functions are recommended for the future use in the diatomics-in-molecules studies of the structure and dynamics of oxygen/hydrogen containing molecular systems.