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Proton Transfer in Concentrated Aqueous Hydroxide Visualized Using Ultrafast Infrared Spectroscopy

Proton Transfer in Concentrated Aqueous Hydroxide Visualized Using Ultrafast Infrared Spectroscopy

Sean T Roberts, Krupa Ramasesha, Poul B Petersen, Aritra Mandal, Andrei Tokmakoff

J Phys Chem A. 2011 Apr 28;115(16):3957-72.

PMID: 21314148

Abstract:

While it is generally recognized that the hydroxide ion can rapidly diffuse through aqueous solution due to its ability to accept a proton from a neighboring water molecule, a description of the OH(-) solvation structure and mechanism of proton transfer to the ion remains controversial. In this report, we present the results of femtosecond infrared spectroscopy measurements of the O-H stretching transition of dilute HOD dissolved in NaOD/D(2)O. Pump-probe, photon echo peak shift, and two-dimensional infrared spectroscopy experiments performed as a function of deuteroxide concentration are used to assign spectral signatures that arise from the OH(-) ion and its solvation shell. A spectral feature that decays on a ∼110 fs time scale is assigned to the relaxation of transiently formed configurations wherein a proton is equally shared between a HOD molecule and an OD(-) ion. Over picosecond waiting times, features appear in 2D IR spectra that are indicative of the exchange of population between OH(-) ions and HOD molecules due to deuteron transfer. The construction of a spectral model that includes spectral relaxation, chemical exchange, and thermalization processes, and self-consistently treats all of our data, allows us to qualitatively explain the results of our experiments and gives a lower bound of 3 ps for the deuteron transfer kinetics.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP12168308	Ammonium-d4 deuteroxide solution		12168-30-8	Price

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