PULLMAN, Wash. — The July 15 issue of Nature magazine, a leading international science
journal, features an article on the work of a research group led by Washington State University
physics professor and Pacific Northwest National Laboratory scientist Lai-Sheng Wang.
The group, led by Wang and his postdoctoral research associate, Xue-Bin Wang,
investigates the properties of multiply-charged anions and was the first to directly observe the
repulsive Coulomb barrier in such anions. In the Nature article, they report the observation of a
long-lived multiply-charged anion which has a negative electron-binding energy.
In ordinary molecules, electrons are kept within their orbits by electrostatic attractions with
positively charged nuclei, thus requiring energy to remove an electron from a molecule.
“Many molecules can bind one extra electron to form so-called anions — molecules with a
negative charge,” said Wang. “However, relatively few molecules are able to bind more than one
extra electron because, according to Coulomb’s law, the extra electrons repel each other,
destabilizing multiply-charged anions. Thus, although multiply-charged anions are common in
solutions and solids, few have been observed in isolated form in free space and they have been
difficult to study.
“One unusual characteristic about multiply-charged anions is the fact that the Coulomb
repulsion within the anion actually sets up a potential barrier that can, in a sense, trap the excess
electrons and provide dynamic stability to such molecular species.”
Wang’s group designed an experiment to make multiply-charged anions in the gas phase
and investigate their properties in a vacuum. In a series of experiments, they directly observed
the repulsive Coulomb barrier in multiply-charged anions. According to Wang, a negative
electron-binding energy has never been observed before, because it cannot exist in neutral or
singly charged species.
“In other words,” said Wang, “the electron is unbound in the newly observed molecule.
This is possible owing to the Coulomb barrier, which is analogous to a dam holding water behind
it. Because of the barrier, the multiply-charged anion stores electrostatic energy, analogous to
the dam that stores hydro-energy. This multiply-charged anion, which has a lifetime of more than
400 seconds, can be viewed as a molecular capacitor and a new energy storage medium.”
Wang has joint appointments at WSU Tri-Cities and the W. R. Wiley Environmental
Molecular Sciences Laboratory at Pacific Northwest National Laboratory and conducts his
research at EMSL. He earned his bachelor’s degree in chemistry from Wuhan University in China
and his doctorate in 1989 from the University of California, Berkeley, where he taught for several
years before taking a postdoctoral position at Rice University in Houston, Texas. He came to
WSU Tri-Cities in 1993, where he serves as Physics Program coordinator. In 1997, he was the first
WSU Tri-Cities professor to be named an Alfred P. Sloan Research Fellow.