Ionized water clusters serve as a fundamental reference model for the development of water oxidation methods in the pursuit of clean energy generation. The 1- to 21- water size regime exhibits multiple structural motifs and driving forces between the hydronium ion, hydroxyl radical, and solvent water species. Within small clusters (n = 2 - 4) the contact pair structure (H3O+--- HO•) is energetically favored.1 Upon the addition of another water, it is energetically favorable for the hydronium and radical to be separated by one interstitial water (H3O+--- H2O --- HO•).1 At 13 waters and above, the attractive force between the hydronium and radical is negligible compared to the solvation energy of the surrounding water molecules, resulting in continual separation.2 These results are fortuitous for solar fuel research - which incorporates the use of an electrolytic cell for O2 and H2 generation - due to a driving force for ion mobility being native to the ionized system, which facilitates charge flow. More fundamentally, this work demonstrates that the contact-pair geometry of the hydronium and radical can be thought of as the dominant species for small systems and at short times, but in the presence of 5 or more waters, separated ion-radical structures are more in tune with condensed-phase characteristics. References: 1. Herr, J. D.; Talbot, J.; Steele, R. P., Structural Progression in Clusters of Ionized Water, (H2O)n=1–5+. The Journal of Physical Chemistry A 2015, 119 (4), 752-766. 2. Herr, J.D.; Steele, R. P., Ion-Radical Pair Separation in Larger Ionized Water Clusters, (H2O)n=6-21+. The Journal of Physical Chemistry A 2015, Under Review.

Ion-radical pair characteristics in oxidized water clusters, (H2O)+n=1-21

251st National Meeting (2016)

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