doi:10.1016/j.cplett.2005.05.084
Copyright © 2005 Elsevier B.V. All rights reserved.
Effect of bromide on the interfacial structure of aqueous tetrabutylammonium iodide: Photoelectron spectroscopy and molecular dynamics simulations
aMax-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, D-12489 Berlin, Germany
bMax-Planck-Institut für Strömungsforschung, Bunsenstr. 10, D-37073 Göttingen, Germany
cInstitute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 16610 Prague 6, Czech Republic
Received 1 March 2005;
revised 3 May 2005.
Available online 15 June 2005.
References and further reading may be available for this article. To view references and further reading you must
purchase this article.
Abstract
Solvation of surface-active tetrabutylammonium iodide (TBAI) in liquid water and in sodium bromide aqueous solution was investigated by VUV photoelectron spectroscopy and by molecular dynamics simulations. The observed signal intensity changes in the photoemission spectra are consistent with the varying propensities of the different ions for the solution interface. While the cations are surface-bound due to hydrophobic interactions, the anions are driven to the vacuum/solution interface by their large polarizability and size. Iodide is more polarizable, and hence more surface-active than bromide, which explains the relatively small decrease of the iodide photoemission signal when TBAI is dissolved in bromide solution.
Fig. 1. Photoelectron spectrum of 0.02 m TBAI, compared to that of 1 m NaBr and a mixture of 1 m NaBr and 0.02 m TBAI aqueous solutions. Excitation energy was 100 eV.
Fig. 2. Typical snapshots from MD simulations of (a) a single TBAI ion pair, and (b) 16 TBAI ion pairs in a slab containing 16 NaBr ion pairs and 863 water molecules. Color coding: TBA+ – light blue and white, iodide – magenta, bromide – gold, sodium – green, water – red and white sticks. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 3. Density profiles of (a) dilute TBAI (single ion pair) and (b) concentrated TBAI (16 ion pairs) in a 1 M NaBr solution across the aqueous slab.