"Is he a dot, or is he a speck,
When he’s underwater does he get wet,
Or does the water get him instead?
Nobody knows: Particle Man."
Those lyrics, from one of the most popular songs by quirky alt-rock band They Might Be Giants, seem apropos to recent research published in Nature Communications, on what exactly happens when electrons get wet. Measurements of the electron affinity of water – the energy gain involved when liquid captures an electron – have historically proved technically challenging.
According to study coauthor Giulia Galli, a professor at the Institute for Molecular Engineering (IME) at the University of Chicago and a senior scientist at Argonne National Laboratory, "Most of the results quoted in the literature as experimental numbers are actually values obtained by combining some measured quantities with crude theoretical estimates."
But models developed by UC San Diego Professor Francesco Paesani, theoretical methods and software developed by Galli’s group and Argonne’s supercomputer have led to new insight.
A key question of the study was whether the liquid binds the electron right away – this determines whether the electron can eventually participate in chemical reactions while inside the liquid. According to study results, the electron is bound with a much smaller energy than previously believed – and this finding led the researchers to revisit a number of other well-accepted data and models about water’s electron affinity.
“We found large differences between the affinity at the surface and in the bulk liquid. We also found values rather different from those accepted in the literature, which prompted us to revisit the full energy diagram of an electron in water," said T.A. Pham, a scientist at Lawrence Livermore National Laboratory (LLNL).
The finding has important consequences for understanding reduction/oxidation reactions in aqueous solutions. These reactions are widespread in both chemistry and biology, providing the framework for understanding phenomena such as how cells break down food for energy and how objects corrode in water. It also may eventually help scientists and engineers to develop better ways of splitting water for chemical processes such as the making of hydrogen fuel. And it may even alter the fundamental understanding of the properties of water itself.