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Azide-water intermolecular coupling measured by two-color two-dimensional infrared spectroscopy
Joanna Borek1, Fivos Perakis, Felix Kläsi
1Physikalisch-Chemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland.
The Journal of Chemical Physics
|June 21, 2012
Summary
Two-color 2D infrared spectroscopy reveals how water molecules hydrogen bond with azide ions. Water molecules near the ion are in a defined environment, but this selectivity is lost as the sample thermalizes.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Chemical Physics
Background:
- Understanding ion-water interactions is crucial for chemical processes.
- Hydrogen bonding dynamics at the molecular level are complex.
- Spectroscopic methods probe molecular vibrations and interactions.
Purpose of the Study:
- To investigate intermolecular coupling between azide ions and water molecules.
- To elucidate the nature of hydrogen bonding between ions and water.
- To utilize two-dimensional infrared (2D IR) spectroscopy for studying solvation shells.
Main Methods:
- Two-color two-dimensional infrared (2D IR) spectroscopy.
- Measuring intermolecular coupling via spectral cross-peaks.
- Analyzing population transfer between vibrational modes (azide and D2O OD-stretch).
Main Results:
- The primary spectral contribution arises from population transfer between azide and D2O vibrations.
- Azide-bound D2O shows a narrow bleach/stimulated emission signal, indicating selectivity for solvation shell water up to ~500 fs.
- A broader excited-state absorption signal for azide-bound D2O was observed, similar to isotope-diluted ice Ih, suggesting potential anharmonicity effects.
Conclusions:
- The study provides insights into the hydrogen bonding of water to azide ions.
- The experimental method demonstrates selectivity for solvation shell water molecules.
- The observed spectral asymmetry may be linked to the anharmonicity of the OD potential in water.
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