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arXiv · 1307.6075

Femtosecond study of the effects of ions on the reorientation dynamics of water

Sietse T. van der Post·Stefan Scheidelaar·Huib J. Bakker
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Abstract

We study the effects of ions on the reorientation dynamics of liquid water with polarization-resolved femtosecond mid-infared spectroscopy. We probe the anisotropy of the excitation of the O-D stretch vibration of HDO molecules in solutions of NaCl, NaI and tetra-alkylammonium bromide salts in 8 percent HDO:H2O. We find that the reorientation O-D groups of HDO molecules hydrating the Cl- and I- anions occurs on two different time scales with time constants of 2pm0.3 ps and 9pm2 ps. The fast component is due to a wobbling motion of the O-D group that keeps the hydrogen bond with the halogenic anion intact. For solutions of tetra-alkylammonium bromide salts we observe a very strong slowing down of the reorientation of water that is associated with the hydration of the hydrophobic alkyl groups of the tetra-alkylammonium ions.

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Sietse T. van der Post, Stefan Scheidelaar, Huib J. Bakker. 2013-07-23. Femtosecond study of the effects of ions on the reorientation dynamics of water. https://doi.org/10.1016/j.molliq.2012.05.014

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