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Physical Sciences
Research Highlights

December 2006

Discovering the Details of Dissolution

New combination of technologies gives insights into one of the most fundamental chemical reactions


Liquid molecules
Researchers at PNNL brought together a combination of theoretical and experimental approaches to determine the number, relative positions and motions of the liquid molecules surrounding ions.
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Results: Ions in a liquid are like celebrities at a movie opening; surrounded by fans who jostle each other to get as close as the velvet ropes around the red carpet will allow. So it is with ions in water or other liquids. Researchers at Pacific Northwest National Laboratory brought together an unusual combination of theoretical and experimental approaches to determine the number, relative positions and motions of the liquid molecules surrounding the ions. This work is an initial step in developing fundamental principles that explain how ions move in complex systems.

Why it matters: While table salt dissolving in water or another solvent to form positive and negative ions may seem to be the province of elementary school science classes, the knowledge of the structure formed by the ion and the first layer of solvent molecules that surround it has broad applications, from understanding how pollutants move in the soil to how neurotransmitters work in the brain.

Further, the researchers hope other scientists can apply the novel combination of approaches developed through their work to other molecular studies. This broad applicability is why their paper was selected to grace the cover of the Journal of Physical Chemistry, Part B.

Methods: By combining two techniques that are not commonly used together, the team created simulations, or short video clips, that show the location of the ions and the water molecules. The first technique, known as Extended X-Ray Absorption Fine Structure spectroscopy, uses X-rays to probe the relative positions of atoms in a solution. The second technique uses advanced calculations and molecular modeling to simulate the structure and motion of relevant systems. Then, the team showed the accuracy of the molecular modeling by comparison to the x-ray spectroscopic measurement.

What’s next: The researchers hope to continue exploring the relationship between ions and liquids.

Collaborators: The team collaborated with researchers at the Advanced Photon Source at Argonne National Laboratory.

Funding agency: The U.S. Department of Energy Basic Energy Sciences, Chemical Sciences Division, funded this research at PNNL and Argonne National Laboratory’s Advanced Photon Source.

Citation: Dang, LX, GK Schenter, VA Glezakou, and JL Fulton. 2006. “Molecular simulation analysis and x-ray absorption measurement of Ca2+, K+ and Cl- ions in solution.” Journal of Physical Chemistry Part B 110(47):23644.

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