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

Abstract

Unlike most polar liquids, excess electrons in liquid CH3CN take on two distinct forms – solvated electrons (esolv–) and solvated molecular anions – that are in equilibrium with each other. We find that excitation of esolv– 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 esolv–. We also find that esolv– 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 esolv– in liquid CH3CN have an inhomogeneously broadened spectrum, demonstrating that these electrons almost certainly reside in a cavity. Because there is no polarized hole-burning for esolv– in water or methanol, these results have important implications for the nature of excess electrons in all polar liquids.