Hydrated Excess Protons in Acetonitrile/Water Mixtures: Solvation Species and Ultrafast Proton Motions

Achintya Kundu, Fabian Dahms, Benjamin P. Fingerhut, Erik T.J. Nibbering, Ehud Pines, Thomas Elsaesser

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


The solvation structure of protons in aqueous media is highly relevant to electric properties and to proton transport in liquids and membranes. At ambient temperature, polar liquids display structural fluctuations on femto- to picosecond time scales with a direct impact on proton solvation. We use two-dimensional infrared (2D-IR) spectroscopy to follow proton dynamics in acetonitrile/water mixtures with the Zundel cation H 5 O 2 + prepared in neat acetonitrile as a benchmark. The 2D-IR spectra of the proton transfer mode of H 5 O 2 + demonstrate stochastic large-amplitude motions in the double-minimum proton potential, driven by fluctuating electric fields. In all cases, the excess proton is embedded in a water dimer, forming an H 5 O 2 + complex as the major solvation species. This observation is rationalized by quantum mechanics/molecular mechanics molecular dynamics simulations including up to four water molecules embedded in acetonitrile. The Zundel motif interacts with its closest water neighbor in an H 7 O 3 + unit without persistent proton localization.

Original languageEnglish
Pages (from-to)2287-2294
Number of pages8
JournalJournal of Physical Chemistry Letters
Issue number9
StatePublished - 2 May 2019

ASJC Scopus subject areas

  • General Materials Science
  • Physical and Theoretical Chemistry


Dive into the research topics of 'Hydrated Excess Protons in Acetonitrile/Water Mixtures: Solvation Species and Ultrafast Proton Motions'. Together they form a unique fingerprint.

Cite this