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Viscosity Dependence of the Ultrafast Vibrational Dynamics of Borohydride in NaOH Solutions: Crowding Effect on Dihydrogen Bonds

preprint
submitted on 18.09.2019 and posted on 23.09.2019 by Clinton Johnson, Kai C. Gronborg, Thomas Brinzer, Zhe Ren, Sean Garrett-Roe

Two-dimensional infrared spectroscopy (2D-IR) probes the local solvent structure and dynamics of the nu3 mode (BH antisymmetric stretch) of borohydride (BH4- ) in aqueous solution. The 2D-IR spectra of the BH stretches have broad and overlapping bands. Vibrational energy relaxation occurs on a 2 ps timescale. Energy that is initially deposited in BH stretching modes and directly in the solvent generates a long lived hot ground state. Before the hot ground state appears, some indications of intramolecular vibrational energy redistribution are observed. The solvent viscosity was varied (1.5–6 cP) by increasing the hydroxide concentration (0.1–7 M). Within the vibrational lifetime of the BH stretching modes, the rate of structural relaxation slows proportionally to the viscosity due to the overlap of the ions’s solvation shells.

Funding

CHE1454105

History

Email Address of Submitting Author

caj52@pitt.edu

Institution

University of Pittsburgh

Country

United States of America

ORCID For Submitting Author

0000-0002-4141-9495

Declaration of Conflict of Interest

no conflict of interest

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