Trapped Electrons at the Amorphous Solid Water/Vacuum Interface as Possible Reactants in a Water Splitting Reaction

Abstract

The dynamics and energetics of electrons in water impacts diverse fields, from electrochemistry to astrochemistry. In the present experiments, long-lived, low-energy, electronic states are observed at the amorphous solid water (ASW)/vacuum interface with decay times on the order of seconds, orders of magnitude longer than solvated electron states observed in the ASW bulk. The formation, relaxation, and reactivity of these trapped electrons were investigated using two-photon photoemission of >15 bilayers of amorphous D2O adsorbed on the Cu(111) surface. The decay time of the trapped electron signal is approximately 16 s. This extraordinarily long lifetime allows for a reaction between trapped electrons and the ASW surface, producing hydroxide anions and molecular hydrogen at the interface. This reaction is observed by a decrease of the trapped electron population and a concomitant increase of the work function during ultraviolet light exposure. The low-energy electron reactivity at the ASW/vacuum interface has profound implications for astrochemistry due to the prevalence of ASW in space.