Electron Spectroscopy of Aqueous Solution Interfaces Reveals Surface Enhancement of Halides

It has been suggested that enhanced anion concentrations at the liquid/vapor interface of airborne saline droplets are important to aerosol reactions in the atmosphere. We report ionic concentrations in the surface of such solutions. Using x-ray photoelectron spectroscopy operating at near ambient p...

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Bibliographic Details
Published in:Science (American Association for the Advancement of Science) 2005-01, Vol.307 (5709), p.563-566
Main Authors: Ghosal, Sutapa, Hemminger, John C, Bluhm, Hendrik, Mun, Bongjin Simon, Hebenstreit, Eleonore L. D, Ketteler, Guido, Ogletree, D. Frank, Requejo, Felix G, Salmeron, Miquel
Format: Article
Language:English
Subjects:
Analysis
Anions
Aqueous solutions
Chemical composition and interactions. Ionic interactions and processes
Chemistry
Climate
Earth, ocean, space
Electron spectroscopy
Electrons
Exact sciences and technology
External geophysics
Halides
Ions
Kinetics
Mars
Meteorology
Molecular Structure
Observations
Organic Chemistry
Particles and aerosols
Photoelectrons
Relative humidity
Salt
Salts
Solution (Chemistry)
Solutions (Chemistry)
Spectroscopy
Surface chemistry
Tropospheric chemistry
Water
Water pressure
Water vapor
X-rays
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Summary:It has been suggested that enhanced anion concentrations at the liquid/vapor interface of airborne saline droplets are important to aerosol reactions in the atmosphere. We report ionic concentrations in the surface of such solutions. Using x-ray photoelectron spectroscopy operating at near ambient pressure, we have measured the composition of the liquid/vapor interface for deliquesced samples of potassium bromide and potassium iodide. In both cases, the surface composition of the saturated solution is enhanced in the halide anion compared with the bulk of the solution. The enhancement of anion concentration is more dramatic for the larger, more polarizable iodide anion. By varying photoelectron kinetic energies, we have obtained depth profiles of the liquid/vapor interface. Our results are in good qualitative agreement with classical molecular dynamics simulations. Quantitative comparison between the experiments and the simulations indicates that the experimental results exhibit more interface enhancement than predicted theoretically.
ISSN:0036-8075
1095-9203
DOI:10.1126/science.1106525