Experimental and computational study of isotopic effects within the Zundel ion

Isotopic effects are discussed for protonated water in the Zundel form. In an ‘isolated’ deuterated Zundel ion, for a single H the center position has enhanced probability. Experimental studies focused on crystalline ( H 5 O 2 + ) ( Br - ) and its isotopic variants. For a 25% H/75% D mixture at 80 K, the probability of H occupying the central position of the Zundel ion exceeds statistical by a factor ∼2.3. Diffusion Monte Carlo results indicate energy ∼170 cm−1 lower for the isotopomer with H at the ion center. DFT-based normal-mode analysis and on-the-fly molecular dynamics yield infrared spectra that are consistent with experiment.