How do counterions and cavities control electron transfer between atoms in liquids?
Molecular liquids differ from each other not only in their ability to make or accept hydrogen bonds and their polarity but also in their intrinsic packing. We have found that the way a solvent packs can have a dramatic effect on the dynamics of electron transfer reactions. Using a combination of nonadiabatic mixed quantum/classical molecular dynamics simulations and ultrafast pump-probe spectroscopy, we show that a highly unusual packing motif in liquid THF makes charge transfer dynamics in this solvent quite different from those in other solvent such as water. We find that even far from its critical point, liquid THF is naturally full of holes that have the right polarity and solvent structure to easily trap an excess electron; the presence of these holes has important implications for charge-transfer-to-solvent (CTTS) dynamics. We also find that the way in which weakly polar solvents such as THF distribute counterions around a reacting solute can dramatically alter not only the rate
