Hydration and mobility of HO-(aq)

• Main Authors: Asthagiri, D, Pratt, Lawrence Riley, Kress, J D, Gomez, M A
• Format: Conference Proceeding
• Language: English
• Published: United States 31.10.2002
• Subjects: ANIONS; AQUEOUS SOLUTIONS; DILUTION; DISTRIBUTION; HYDRATION; HYDROXIDES; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; PROTONS; TRANSPORT; WATER
• ISSN: 0027-8424; 1091-6490

The hydroxide anion plays an essential role in many chemical and biochemical reactions. But questions of its hydration state and transport in water are currently controversial. Here we address this situation using the quasi-chemical theory of solutions. The simplest such approach suggests that HO [H20]3- is the most probable species at infinite dilution in aqueous solution under standard conditions, followed by the HO . [H20]2- and HO . [HzO]- forms which are close together in stablity. HO . [H20]4- is less stable, in contrast to recent proposals that the latter structure is the most stable hydration species in solution. Ab initio molecular dynamics results presented here support the dominance of the tri-hydrated form, but that the population distribution is broad and sensitive to solution conditions. On the basis of these results, the mobility of hydroxide can be simply that of a proton hole. This contrasts with recent proposals invoking the interconversion of a stable 'trap' structure HO . [H20]4- to HO . [H20]3- as the rate determining step in the transport process.