On the connection between proton transport, structural diffusion, and reorientation of the hydrated hydroxide ion as a function of temperature

The properties of the hydrated hydroxide ion OH − (aq) stand in sharp contrast to those of most other aqueous ions. Chief among these is its anomalously high mobility, which is shared only by the aqueous hydronium ion H 3 O + (aq). However, while the transport mechanism of H 3 O + (aq) is now well understood, the details of OH − (aq) diffusion at ambient conditions are just beginning to emerge, and the effects of temperature on the transport mechanism remain largely unelucidated. Here, we undertake an ab initio molecular dynamics study of the effect of temperature on the solvation and transport of OH − (aq). In addition to revealing new details of the transport process, our analysis provides an explanation for the experimentally observed temperature dependence of the OH − (aq) reorientation time. The calculations reveal a suppression of proton transfer events that underly the structural diffusion process caused by a pronounced change in the population of dominant OH − (aq) solvation complexes.