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17 March 2000 Z .Chemical Physics Letters 319 2000 247252

Summary: 17 March 2000
Z .Chemical Physics Letters 319 2000 247­252
Mechanism of hydroxide mobility
Noam Agmon )
Department of Physical Chemistry and the Fritz Haber Research Center, The Hebrew UniÕersity, Jerusalem 91904, Israel
Received 29 November 1999; in final form 15 January 2000
A suggested mechanism for hydroxide mobility in water identifies the rate limiting step as a cleavage of a second shell
y Z . Z .y Z .hydrogen bond which converts a H O ion triply coordinated hydroxide to HOHOH deprotonated water dimer .7 4
Proton transfer is enabled by an additional O­O bond contraction, not required in H Oq
. This explains why the activation5 2
energy for hydroxide mobility is larger than that of proton mobility by about 0.5 kcalrmol. The transfer cycle is terminated
by hydrogen-bond formation to the other oxygen center. Available experimental data, and most of the computational results,
can be rationalized in the framework of the above model. q 2000 Elsevier Science B.V. All rights reserved.
1. Introduction
The proton and hydroxide-ion are by far the
fastest diffusing ions in liquid water. At room tem-
perature, proton mobility is 4.5 times larger than that
Z q. Z y.of the most mobile cation Rb or anion Br ,


Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem


Collections: Chemistry