An Accurate Quartic Force Field and Fundamental Frequencies for the Ozonide Anion: A Rare Positive Anharmonicity for the Antisymmetric Stretch

The CCSD(T) method has been used to compute a highly accurate quartic force field and fundamental frequencies for all 16O and 18O isotopomers of the ozonide anion. The CCSD and CASPT2 methods have also been used to verify the reliability of the CCSD(T) fundamental frequencies. The computed fundamental frequencies are in agreement with gas-phase experiments, but disagree with matrix isolation experiments for the antisymmetric stretch, ν3. CASPT2 calculations show that the antisymmetric part of the O3- potential surface is sensitive to the external environment. It is concluded that the antisymmetric stretch exhibits a significant matrix shift in the matrix isolation experiments and that the matrix environment is not representative of the gas-phase environment for ozonide anion. It is hoped that the theoretical data provided here will aid in the interpretation of future high-resolution gas-phase experiments.