Web Release Date: April 20,
Surface Segregation of Dissolved Salt Ions
and
Technische Universität Clausthal, Institut für Physik und Physikalische Technologien, Leibnizstr. 4,
D-38678 Clausthal-Zellerfeld, Germany, Chemical Sciences Division, Pacific Northwest National Laboratory,
Richland, Washington 99352, U.S.A., and Institute of Organic Chemistry and Biochemistry, Academy of
Sciences of the Czech Republic, and Center for Biomolecules and Complex Molecular Systems,
Flemingovo n
m. 2, 16610 Prague 6, Czech Republic
Received: March 8, 2006
Abstract:
Surface segregation of iodide, but not of fluoride or cesium ions, is observed by a combination of metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS(HeI)) of amorphous solid water exposed to CsI or CsF vapor. The same surface ionic behavior is also derived from molecular dynamics (MD) simulations of the corresponding aqueous salt solutions. The MIES results show the propensity of iodide, but not fluoride, for the surface of the amorphous solid water film, providing thus strong evidence for the suggested presence of heavier halides (iodide, bromide, and to a lesser extent chloride) at the topmost layer of aqueous surfaces. In contrast, no appreciable surface segregation of ions is observed in methanol, neither in the experiment nor in the simulation. Furthermore, the present results indicate that, as far as the thermodynamic aspects of solvation of alkali halides are concerned, amorphous solid water and methanol surfaces behave similarly as surfaces of the corresponding liquids.
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