Terahertz echoes reveal the inhomogeneity of aqueous salt solutions

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 mona...

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Bibliographic Details
Published in:Nature chemistry 2017-03, Vol.9 (3), p.273-278
Main Authors: Shalit, Andrey, Ahmed, Saima, Savolainen, Janne, Hamm, Peter
Format: Article
Language:English
Subjects:
140/125
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Analytical Chemistry
Biochemistry
Cations
Chemistry
Chemistry/Food Science
Hydrogen
Inorganic Chemistry
Organic Chemistry
Physical Chemistry
Salts
Spectroscopy
Viscosity
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Summary: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 t 1  =  t 2 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. Ultrafast 2D Raman-THz spectroscopy has been applied to investigate the dynamics of the hydrogen-bond networks in aqueous salt solutions. It was demonstrated that the degree of inhomogeneity of the intermolecular modes of the liquid correlates with the structure-making capability of the cation.
ISSN:1755-4330
1755-4349
DOI:10.1038/nchem.2642