Can Electric Fields Drive Chemistry for an Aqueous Microdroplet?

Abstract Reaction rates of common organic reactions have been reported to increase by one to six orders of magnitude in aqueous microdroplets compared to bulk solution, but the reasons for the rate acceleration are poorly understood. We investigate the role of electric fields at water droplet surfaces that might explain the promotion of unusual reactive chemistry, along with changes in electric field profiles as a function of excess charge to model the electrospray fragmentation process. We find that electric field alignments along free O-H bonds at the surface yield field strength distributions that are ~30 MV/cm larger on average than that found for O-H bonds in the interior of the water droplet, consistent with greater surface reactivity. We emphasize the importance of both nuclear and electronic effects at the surface, and the non-linear coupling of intramolecular solute polarization with intermolecular solvent modes, as a necessary feature for predicting the higher field strengths at water droplet surfaces.