Trap-Seeking or Trap-Digging? Photoinjection of Hydrated Electrons into Aqueous NaCl Solutions

It is well-known that when excess electrons are injected into an aqueous solution, they localize and solvate in similar to 1 ps. Still debated is whether localization occurs via trap-digging, in which the electron carves out a suitable localization site, or by trap-seeking, where the electron prefers to localize at pre-existing low-energy trap sites in solution. To distinguish between these two possible mechanisms, we study the localization dynamics of excess electrons in aqueous NaCl solutions using both ultrafast spectroscopy and mixed quantum-classical molecular dynamics simulations. By introducing pre-existing traps in the form of Na + ions, we can use the cation-induced blue-shift of the hydrated electron's absorption spectrum to directly monitor the site of electron localization. Our experimental and computational results show that the electron prefers to localize directly at the sites of Na+ traps; the presence of concentrated electrolytes otherwise has little impact on the way trap-seeking hydrated electrons relax following injection.

Automated summary

By using ultrafast spectroscopy and molecular dynamics simulations, the localization dynamics of excess electrons in aqueous NaCl solutions are investigated. The results show that the electrons prefer to localize at pre-existing trap sites, and the presence of concentrated electrolytes has little impact on the localization behavior.