Proton Transfer in Concentrated Aqueous Hydroxide Visualized using Ultrafast Infrared Spectroscopy
Author(s)Roberts, Sean Thomas; Ramasesha, Krupa; Petersen, Poul B.; Mandal, Aritra; Tokmakoff, Andrei
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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/D2O. 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.
DepartmentMassachusetts Institute of Technology. Department of Chemistry
Journal of Physical Chemistry A
American Chemical Society
Roberts, Sean T. et al. “Proton Transfer in Concentrated Aqueous Hydroxide Visualized Using Ultrafast Infrared Spectroscopy.” The Journal of Physical Chemistry A 115.16 (2011): 3957–3972.
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