Proton Defect Solvation and Dynamics in Aqueous Acid and Base

Abstract

Keywordsdiffusion; hydronium; hydroxide; proton transport; water chemistry Our current understanding of proton defects in bulk water, depends heavily on the interplay between scattering experiments and ab initio simulations, both of which require such high ion concentrations that the solvation shells overlap and counterion effects become significant. Here, we overcome these limitations by using LEWIS, an intuitive new model of reactive and polarizable water that enables the simulation of a statistically reliable number of proton hopping events in aqueous acid and base at concentrations of practical interest (0.1 M). LEWIS predicts radial distribution functions (rdf's) that are similar to those obtained by density functional theory (DFT) and relative diffusion rates for excess protons and proton holes that compare well with experiment. The simulations show that proton transfers occur primarily between persistent special pairs, a Zundel-type species in the case of an excess proton and its analog in the case of a proton hole. The simulations also show that, relative to vehicular diffusion, proton transfers contribute more significantly to total defect diffusion in acid than in base.