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Chemistry Colloquium: April 15


Professor Gerrik Lindberg
Northern Arizona University

April 15, 2015
11:00 am – 12:00 pm
C-121

“‘Ions at the Air-Water Interface: Determining the pH of Interfacial Water”

Abstract: Significant effort has been invested in understanding the mechanistic details governing the propensity of ions to surfaces, which has since evolved into a grand challenge to determine the pH of interfacial water. Using computationally efficient multistate simulations, the affinity of HO- and H+ ions for the air-water interface is studied with focus on the coupling of these ions to solvent fluctuations. These reactive simulations efficiently capture the bond breaking and forming processes that are important for correctly describing HO- and H+ transport. In these simulations, HO- is found to be repelled from the interface. This repulsion of HO- is characterized by a reduction in the number of solvating water molecules, which creates an enthalpic penalty as the ion approaches the interface. The influence of a weak hydrogen bond donated from water to the protonated oxygen, known to play a critical role in proton transport, is examined. The excess proton is attracted to the interface, which is correlated with a favorable enthalpic contribution and is consistent with eliminating the disruption in the hydrogen bond network caused by H3O+ serving as a weak hydrogen-bond acceptor.

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