Ab initio path integral simulation study on 16O/18O isotope effect in water and hydronium ion

An ab initio path integral molecular dynamics simulation has been performed to study the 16O and 18O isotopomers for a water molecule and a hydronium ion at temperature 300 K. The average O–H bond length of H218O molecule is slightly shorter than that of H216O molecule, while that of H318O+ is slightly longer than that of H316O+. For hydronium ions, the Walden inversion of H318O+, as well as D316O+, is found to be more restrained than that of H316O+. The isotope effect in the electronic structure and thermochemical properties for these isotopomers are also shown.