Using cluster studies to approach the electronic structure of bulk water: Reassessing the vacuum level, conduction band edge, and band gap of water

Aqueous cluster studies have lead to a reassessment of the electronic properties of bulk water, such as band gap, conduction band edge, and vacuum level. Using results from experimental hydrated electron cluster studies, the location of the conduction band edge relative to the vacuum level (often called the V0 value) in water has been determined to be −0.12 eV⩽V0⩽0.0 eV, which is an order of magnitude smaller than most experimental values in the literature. With V0=−0.12 eV and making use of the calculated solvation energy of OH in water, the band gap of water is determined to be 6.9 eV. Again, this is smaller than many literature estimates. In the course of this work, it is shown that due to water’s ability to reorganize about charge (1) photoemission thresholds of water or anionic defects in water do not determine the vacuum level, and (2) there is almost no probability of accessing the bottom of the conduction band of water with a vertical/optical process from water’s valence band. The results are presented in an energy diagram for bulk water which shows the utility of exploring the conduction band of water as a function of solvent polarization.