Research by a UCLA team led by Professor Benjamin Schwartz and graduate student William Borrelli is featured on the front cover of this week’s Journal of Physical Chemistry Letters, a leading American Chemical Society journal that covers all aspects of physical chemistry. The highlighted study shows that models in which an extra electron is surrounded by water molecules that are able to fluctuate better explains experimental observations of the electron solvation entropy, while models in which the electron does not have a flexible cavity give qualitatively incorrect predictions.
Scientists have long tried to understand what happens when an extra electron sits in liquid water — producing a so-called a “hydrated electron.” The water molecules around it rearrange and move in unusual ways, and experiments show this creates an unexpectedly large increase in disorder (called the solvation entropy). In this study, the researchers used advanced computer simulations to test different ways of modeling how the electron is solvated by water. Although most models have the excess electron sitting in a cavity in liquid water, they found that models where the cavity is soft and flexible best match experiment, even though such models still don’t fully capture the full magnitude of the solvation entropy. Other models — where the electron either does not reside in a cavity or sits in a more rigid cavity — give qualitatively wrong results. Overall, the findings show that understanding how water molecules move and organize immediately around the electron is key to predicting its behavior.
Penny Jennings, UCLA Department of Chemistry & Biochemistry, penjen@g.ucla.edu.
