The Hydrated Electron at the Surface of Neat Liquid Water Appears To Be Indistinguishable from the Bulk Species

Abstract

Experiments have suggested that the aqueous electron, e(-)(aq), may play a significant role in the radiation chemistry of DNA. A recent measurement of the energy (below vacuum level) of the putative "interfacial" hydrated electron at the water/vacuum interface, performed using liquid microjet photoelectron spectroscopy, has been interpreted to suggest that aqueous electrons at the water/biomolecule interface may possess the appropriate energetics to induce DNA strand breaks, whereas e(-)(aq) in bulk water lies too far below the vacuum level to induce such reactions. Other such experiments, however, find no evidence of a long-lived feature at low binding energy. We employ a variety of computational strategies to demonstrate that the energetics of the hydrated electron at the surface of neat liquid water are not significantly different from those of e(-)(aq) in bulk water and as such are incompatible with dissociative electron attachment reactions in DNA. We furthermore suggest that no stable interfacial species may exist at all, consistent with the interpretation of certain surface-sensitive spectroscopy measurements, and that even if a short-lived, metastable species does exist at the vacuum/water interface, it would be extremely difficult to distinguish, experimentally, from e(-)(aq) in bulk water, using either optical absorption or photoelectron spectroscopy.