Revealing excess protons in the infrared spectrum of liquid water

Abstract

The most common species in liquid water, next to neutral H${}_2$O molecules, are the H${}_3$O${}^{+}$ and OH${}^{-}$ ions. In a dynamic picture, their exact concentrations depend on the time scale at which these are probed. Here, using a spectral-weight analysis, we experimentally resolve the fingerprints of the elusive fluctuations-born short-living H${}_3$O${}^{+}$, DH${}_2$O${}^{+}$, HD${}_2$O${}^{+}$, and D${}_3$O${}^{+}$ ions in the IR spectra of light (H${}_2$O), heavy (D${}_2$O), and semi-heavy (HDO) water. We find that short-living ions, with concentrations reaching $\sim 2\%$ of the content of water molecules, coexist with long-living pH-active ions on the picosecond timescale, thus making liquid water an effective ionic liquid in femtochemistry.

References in corpus (1)

• Radiolysis of water confined in porous silica: A simulation study of the physicochemical yields

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