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Large-amplitude transfer motion of hydrated excess protons mapped by ultrafast 2D IR spectroscopy

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Science  13 Jul 2017:
eaan5144
DOI: 10.1126/science.aan5144

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Abstract

Solvation and transport of excess protons in aqueous systems play a fundamental role in acid-base chemistry and biochemical processes. Here, we map ultrafast proton excursions along the proton transfer coordinate by 2D infrared (IR) spectroscopy, both in bulk water and in a Zundel cation (H5O2)+ motif selectively prepared in acetonitrile. Electric fields from the environment and stochastic hydrogen bond motions induce fluctuations of the proton double-minimum potential. Within the lifetime of a particular hydration geometry, the proton explores a multitude of positions on a sub-100 fs time scale. The proton transfer vibration is strongly damped by its 20 to 40 fs population decay. Our results suggest a central role of Zundel-like geometries in aqueous proton solvation and transport.

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