PHYS 726 |
| Recent experimental and computational studies have shown that protons in ice greatly prefer sites at or very near the ice surface and that this behavior resembles that of liquid water [1]. Isotopic exchange-rate data, that inter-relate the proton activity at the surface and in the interior of ice nanocrystals, have been measured for pure ice and with sub-monolayer (sub-ML) amounts of weak acid and base adsorbates. The exchange rates, directly determined by the proton activity, are obtained from FTIR spectroscopy of the conversion of isolated D2O to isolated HDO units within and at the surface of the particles. Both the interior and the surface proton activity can be adjusted by orders of magnitude using sub-ML amounts of acid and base adsorbates. The influence of ammonia is particularly informative. As previously observed for the interior of thick ice films [2], a trace of adsorbed ammonia thoroughly stops both the interior and the surface proton activity of ice nanocrystals. 1. V. Buch, A. Milet, R. Vacha, P. Jungwirth, J. P. Devlin, submitted. 2. J. P. Devlin, in "Proton Transfer in Hydrogen-Bonded Systems" NATO ASI Series, 1992, Vol. 291, pp 249 – 260, ed. T. Bountis (Plenum Press, New York).
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Hydration: From Clusters to Aqueous Solution
1:20 PM-5:00 PM, Thursday, August 23, 2007 BCEC -- 159, Oral
Division of Physical Chemistry |