Surface segregation of dissolved salt ions.

Area of Science:

• Physical Chemistry
• Surface Science
• Computational Chemistry

Background:

• Understanding ion behavior at aqueous interfaces is crucial for various chemical and biological processes.
• Previous studies suggest preferential surface segregation of certain ions at liquid water-vapor interfaces.

Purpose of the Study:

• To investigate the surface segregation of iodide, fluoride, and cesium ions at amorphous solid water interfaces.
• To compare the surface behavior of ions in amorphous solid water with that in methanol.
• To validate experimental findings with molecular dynamics simulations.

Main Methods:

• Metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS(HeI)) were used to study amorphous solid water films exposed to CsI or CsF vapor.
• Molecular dynamics (MD) simulations were performed on corresponding aqueous salt solutions to model surface behavior.

Main Results:

• Iodide ions showed significant surface segregation on amorphous solid water, while fluoride and cesium ions did not.
• Experimental results were consistent with MD simulations, confirming iodide's propensity for the water surface.
• No significant ion surface segregation was observed for methanol in either experiments or simulations.

Conclusions:

• Amorphous solid water surfaces exhibit preferential segregation of iodide ions, supporting theories about heavier halide accumulation at aqueous interfaces.
• The surface behavior of alkali halides in amorphous solid water and methanol is thermodynamically similar to their liquid counterparts.
• These findings provide insights into the unique interfacial properties of water and its interactions with ions.