Gas-phase proton affinity of ozone: a computational test of the experimental mechanism

Extended ab initio calculations are carried out for the isolated ozone molecule, in its ground electronic state, and for its protonated adduct. For both systems, the corresponding nuclear geometries of lowest total energies are obtained by multidimensional optimization and different levels of basis set quality and correlation correction are examined in the two cases. The final results provide very good accord between gas-phase protonation energy data and calculated quantities. The extensive numerical experiments clearly underline the need for balanced correlation treatments in systems where both static and dynamic correlation effects are important. They further indicate that the existing kinetics experiments on the gas-phase proton affinity of O-3 are not likely to involve the electron transfer channel via a sampling of the conical intersection configuration space that exists in this system. (C) 2001 Elsevier Science B.V. All rights reserved.