Ab Initio Potential Energy Surface and Vibrational Energies of H3O+ and Its Isotopomers

We report a new full dimensional potential energy surface for the hydronium ion (H 3 O + ). This surface is constructed by a least-squares fit of ab initio electronic energies obtained using the CCSD(T) method with an aug-cc-pVTZ basis set, augmented by some calculations using an aug-cc-pVQZ basis set. The calculated inversion barrier is 693 cm -1 . Full dimensional vibrational calculations are reported using the new surface for H 3 O +, D 3 O +, H 2 DO +, and HD 2 O + using the codes RVIB4 and MULTIMODE. Comparison with all available experimental data on both splittings and vibrational energies shows significant improvement over our previous calculations using the OSS3(p) potential. A number of vibrational band energies and splittings not measured experimentally are reported for D 3 O +, HD 2 O +, and H 2 DO + .