Nature of Excess Electrons in Polar Fluids: Anion-Solvated Electron Equilibrium and Polarized Hole-Burning in Liquid Acetonitrile

Unlike most polar liquids, excess electrons in liquid CH 3 CN take on two distinct forms – solvated electrons ( e solv – ) and solvated molecular anions – that are in equilibrium with each other. We find that excitation of e solv – leads to a short-lived excited state that has no effect on the equilibrium but that excitation of the molecular anion instantaneously leads to the production of new e solv – . We also find that e solv – produced by excitation of dimer anions relocalize to places far enough from their original location to alter their recombination dynamics. Finally, we show using polarized transient hole-burning that e solv – in liquid CH 3 CN have an inhomogeneously broadened spectrum, demonstrating that these electrons almost certainly reside in a cavity. Because there is no polarized hole-burning for e solv – in water or methanol, these results have important implications for the nature of excess electrons in all polar liquids.