Understanding the Structure and Dynamics of Solvated Electrons Using Ultrafast Spectroscopy and Quantum Simulation Methods

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

In this project funded by the Chemical Structure, Dynamics and Mechanisms-A Program (CSDM-A) of the Chemistry Division, Professor Benjamin J. Schwartz and his students at the University of California-Los Angeles are using a combination of experimental and theoretical techniques to unravel the structure and behavior of solvated electrons. Salt water is a common example of an electrolyte, which contains dissolved positively charged cations (sodium, Na+) and negatively anions (chloride, Cl-). Under certain circumstances, it is possible for electrons (e-) to be dissolved in a liquid. Such solutions are more difficult to understand and predict, because electrons are thousands of times less massive than atoms and molecules, and are much more mobile. The Schwartz group is using lasers which produce extremely short pulses of light (30 - 40 quadrillionths of a second) to capture the motions and energies of these fast moving electrons. The experimental results are being compared with quantum mechanical calculations (quantum mechanics is a type of math that deals with extremely small objects like electrons, atoms, and molecules), and computer simulations of the motions of the liquid molecules that "solvate" the electron. The broader impacts of this work include a better understanding of radiation chemistry (reactions with solvated electrons make high energy radiation dangerous to living organisms) and electron transfer reactions (such as those in both biology and batteries). Because this project combines experiment and theory, undergraduate and graduate student researchers receive a rich experience in experimental chemistry, laser technology, and computer programming, all of which are increasingly valuable for the modern science workforce. The Schwartz group also works with high school teachers in the Los Angeles area to enrich their science classes through lectures and the development of experimental lesson kits. The experimental focus of the project uses ultrafast spectroscopy to study the properties of solvated electrons. Ultrafast spectroscopy takes advantages of pulses of light that are extremely short (~tens of femtoseconds), providing a means to "stop the motion" of the electrons on the time scale with which molecules move in room temperature liquids. The theoretical focus of the project is based on mixed quantum/classical simulations. Here, quantum mechanics is used to describe the properties of the solvated electrons, but the solvent molecules are treated classically. The simulations can be used to calculate the results of the ultrafast spectroscopy experiments, so that together, the combination of experiments and simulations can provide new insights into the structure and reactivity of this interesting and important chemical species. Because solvated electrons involve motions of only a single electron, they also provide a test system to compare the predictions of quantum mechanical simulations directly with the results of laboratory experiments. In addition to the training of undergraduate and graduate students, the Schwartz group also works with high school teachers in the Los Angeles area to enrich their science classes, through lectures and the development of experiment kits. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.