Effect of Bromide on the Interfacial Structure of Aqueous Tetrabutyl-Ammonium Iodide: Photoelectron Spectroscopy and Molecular Dynamics Simulations
نویسندگان
چکیده
Bernd Winter, Ramona Weber, and Ingolf V. Hertel Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, D-12489 Berlin, Germany Manfred Faubel Max-Planck-Institut für Strömungsforschung, Bunsenstr. 10, D-37073 Göttingen, Germany Luboš Vrbka and Pavel Jungwirth Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Complex Molecular Systems and Biomolecules, Flemingovo nam. 2, 16610 Prague 6, Czech Republic Abstract Solvation of surface-active tetrabutyl-ammonium iodide (TBAI) in pure liquid water and in sodium bromide aqueous solution was investigated by photoelectron spectroscopy and by molecular dynamics simulations. Using VUV synchrotron radiation the experimental technique is particularly suitable to investigate the solution surface. The observed anion signal intensity changes in the photoemission spectra, in the presence of bromide, are consistent with the varying propensities of the different ions for the solution interface, analyzed in terms of hydrophobic, polarization, and ion-ion interactions. 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 the smaller bromide, which explains the relatively small decrease of the iodide photoemission signal when TBAI is dissolved in bromide aqueous solution.
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