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Issue 18, 2012
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The combined effect of cations and anions on the dynamics of water

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Abstract

We studied the orientational relaxation of the OD-stretch vibration of HDO molecules in concentrated solutions of alkali-halide salts (NaCl, NaI, CsCl and KI) in isotopically diluted water (4% D2O in H2O), using polarization-resolved femtosecond infrared pump–probe spectroscopy (fs-IR). We were able to distinguish the orientational dynamics of the water molecules solvating the halide ions from the dynamics of the bulk water and the water solvating the cations. We found that the reorientation of the halide-bound molecules shows two strongly different components (2.0 ± 0.3 ps and 9 ± 1 ps), related to a wiggling motion of the OD group hydrogen-bonded to the anion, and rotational diffusion of the molecule over the charged anion surface, respectively. The relative amplitudes of the two components are dependent on the nature of both the anion and cation, and on the concentration. These results show that cations can have a profound effect on the solvation shell dynamics of their counter-ions.

Graphical abstract: The combined effect of cations and anions on the dynamics of water

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Article information


Submitted
05 Dec 2011
Accepted
16 Feb 2012
First published
17 Feb 2012

Phys. Chem. Chem. Phys., 2012,14, 6280-6288
Article type
Paper

The combined effect of cations and anions on the dynamics of water

S. T. V. D. Post and H. J. Bakker, Phys. Chem. Chem. Phys., 2012, 14, 6280
DOI: 10.1039/C2CP23882A

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