Quantum Calculations of Vibrational Energies of H<sub>3</sub>O<sub>2</sub><sup>-</sup> on an ab Initio Potential

We report a full-dimensional potential energy surface for H<sub>3</sub>O<sub>2</sub><sup>-</sup>, based on fitting 66,965 ab initio electronic energies. A major feature of this potential is a barrier of roughly 200 cm<sup>-1</sup> to internal rotation of the two hydroxyl groups about a line connecting the two oxygen atoms and the bridging hydrogen atom. The potential is used in calculations of vibrational energies, performed with the “Reaction Path” version of the code “MULTIMODE”. The results are compared to recent infrared messenger experiments and are used to propose interpretations of the experimental results.