PNNL

Abstract

The isomerization pathway between the energetically low-lying Zundel (Z) and Eigen (E) isomers of the protonated water hexamer, investigated via high level ab initio calculations and a proper treatament of zero point corrections, was found to proceed via a stable intermediate isomer comprising of a four-membered ring with two single acceptor water molecules. The inclusion of vibrational zero-point energy is shown to be important for accurately establishing the relative energy of the three relevant isomers involved in the Z-E isomerization. Diffusion Monte Carlo (DMC) calculations including anharmonic vibrational effects show that all three isomers have well-defined structures for both the all-H and all-D isotopomers. The energetic ordering of the three isotopomers changes upon deuteration. Implications of these results for the vibrational spectra of H+(H2O)6 and D+(D2O)6 are further discussed.