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Terahertz echoes reveal the inhomogeneity of aqueous salt solutions


Shalit, Andrey; Ahmed, Saima; Savolainen, Janne; Hamm, Peter (2016). Terahertz echoes reveal the inhomogeneity of aqueous salt solutions. Nature Chemistry, 9(3):273-278.

Abstract

The structural and dynamical properties of water are known to be affected by ion solvation. However, a consistent molecular picture that describes how and to what extent ions perturb the water structure is still missing. Here we apply 2D Raman–terahertz spectroscopy to investigate the impact of monatomic cations on the relaxation dynamics of the hydrogen-bond network in aqueous salt solutions. The inherent ability of multidimensional spectroscopy to deconvolute heterogeneous relaxation dynamics is used to reveal the correlation between the inhomogeneity of the collective intermolecular hydrogen-bond modes and the viscosity of a salt solution. Specifically, we demonstrate that the relaxation time along the echo direction t1 = t2 correlates with the capability of a given cation to ‘structure’ water. Moreover, we provide evidence that the echo originates from the water–water modes, and not the water–cation modes, which implies that cations can structure the hydrogen-bond network to a certain extent.

Abstract

The structural and dynamical properties of water are known to be affected by ion solvation. However, a consistent molecular picture that describes how and to what extent ions perturb the water structure is still missing. Here we apply 2D Raman–terahertz spectroscopy to investigate the impact of monatomic cations on the relaxation dynamics of the hydrogen-bond network in aqueous salt solutions. The inherent ability of multidimensional spectroscopy to deconvolute heterogeneous relaxation dynamics is used to reveal the correlation between the inhomogeneity of the collective intermolecular hydrogen-bond modes and the viscosity of a salt solution. Specifically, we demonstrate that the relaxation time along the echo direction t1 = t2 correlates with the capability of a given cation to ‘structure’ water. Moreover, we provide evidence that the echo originates from the water–water modes, and not the water–cation modes, which implies that cations can structure the hydrogen-bond network to a certain extent.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:31 October 2016
Deposited On:23 Jan 2017 14:20
Last Modified:22 Feb 2017 02:03
Publisher:Nature Publishing Group
ISSN:1755-4330
Funders:Swiss National Science Foundation (SNF) through the NCCR MUST
Publisher DOI:https://doi.org/10.1038/nchem.2642

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