Ambient Pressure X-ray Photoelectron Spectroscopy and Molecular Dynamics Simulation Studies of Liquid/Vapor Interfaces of Aqueous NaCl, RbCl, and RbBr Solutions

作者：Cheng Ming Hsin; Callahan Karen M; Margarella Alexandria M; Tobias Douglas J^*; Hemminger John C; Bluhm Hendrik; Krisch Maria J

来源：Journal of Physical Chemistry C, 2012, 116(7): 4545-4555.

DOI：10.1021/jp205500h

Ambient pressure X-ray photoelectron spectroscopy (AP-XPS) was used to explore ion behavior at liquid/vapor interfaces of aqueous NaCl, RbCl, and RbBr solutions. Interfacial depth profiles of ions were obtained from XPS spectra at a series of photoelectron kinetic energies. Depth profiles of the ratio of anion to cation show little difference among the solutions. Previously, these depth profiles were determined from the ratio of anion to cation signal-peak areas. However, using molecular dynamics simulations (MD), the individual anion and cation depth profiles are both observed to differ as a function of solution, but the differences are masked when only the anion-to-cation ratios are considered. Using the Cl-/O-water ratio determined from the XPS measurements, surface-enhanced concentrations of Cl- are observed in the NaCl solution, but not in the RbCl solution, in agreement with predictions from MD simulations. We also report studies of aqueous solutions of RbBr. In contrast to an aqueous RbCI solution, our combination of AP-XPS experiments and MD simulations suggests that anion/cation ratios are enhanced at the surface for this system due to the separation of bromide and rubidium in the double layer near the surface, while the interfacial concentration of bromide does not differ considerably from the bulk.

• 出版日期2012-2-23