Observation of a Zundel-like transition state during proton transfer in hydroxide solutions
Name
Roberts-2009-Observation of a Zun.pdf
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Author(s)
Tokmakoff, Andrei
Ramasesha, Krupa
Petersen, Poul B.
Roberts, Sean Thomas
Martinez, Todd J.
Ufimtsev, Ivan S.
Date Issued
July 2009
Journal
Proceedings of the National Academy of Sciences of the United States of America
Publisher
United States National Academy of Sciences
Citation
Roberts, Sean T et al. “Observation of a Zundel-like transition state during proton transfer in aqueous hydroxide solutions.” Proceedings of the National Academy of Sciences 106.36 (2009): 15154-15159. © 2009 National Academy of Sciences
Version
Final published version
Abstract
It is generally accepted that the anomalous diffusion of the aqueous hydroxide ion results from its ability to accept a proton from a neighboring water molecule; yet, many questions exist concerning the mechanism for this process. What is the solvation structure of the hydroxide ion? In what way do water hydrogen bond dynamics influence the transfer of a proton to the ion? We present the results of femtosecond pump-probe and 2D infrared experiments that probe the O-H stretching vibration of a solution of dilute HOD dissolved in NaOD/D[subscript 2]O. Upon the addition of NaOD, measured pump-probe transients and 2D IR spectra show a new feature that decays with a 110-fs time scale. The calculation of 2D IR spectra from an empirical valence bond molecular dynamics simulation of a single NaOH molecule in a bath of H[subscript 2]O indicates that this fast feature is due to an overtone transition of Zundel-like H[subscript 3]O[subscript 2]− states, wherein a proton is significantly shared between a water molecule and the hydroxide ion. Given the frequency of vibration of shared protons, the observations indicate the shared proton state persists for 2–3 vibrational periods before the proton localizes on a hydroxide. Calculations based on the EVB-MD model argue that the collective electric field in the proton transfer direction is the appropriate coordinate to describe the creation and relaxation of these Zundel-like transition states.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
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DOI of Published Version
http://dx.doi.org/10.1073/pnas.0901571106
