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Solvent-Independent Anharmonicity for Carbonyl Oscillators.
Samuel H Schneider1, Huong T Kratochvil2, Martin T Zanni2
1Department of Chemistry, Stanford University , Stanford, California 94305-5012, United States.
The Journal of Physical Chemistry. B
|February 23, 2017
Summary
Vibrational frequency shifts in carbonyls are primarily due to the electric field, not bond polarization. This study confirms the vibrational Stark effect is key for understanding intermolecular interactions.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Computational Chemistry
Background:
- Vibrational frequency shifts in condensed phases are crucial for understanding intermolecular interactions.
- The vibrational Stark effect, caused by the environment's electric field, is proposed as the dominant cause for frequency shifts in carbonyls.
- This contrasts with older theories involving bond polarization or altered resonance structures.
Purpose of the Study:
- To investigate the physical origins of vibrational frequency shifts in carbonyl compounds.
- To test the hypotheses of electric field effects versus bond polarization using solvent-dependent vibrational spectroscopy.
- To assess the solvent dependence of carbonyl bond anharmonicity.
Main Methods:
- Utilized two-dimensional infrared (2D IR) spectroscopy to measure vibrational solvatochromism.
- Employed molecular dynamics (MD) simulations to generate theoretical 2D IR spectra.
- Tested the effects of various solvents, including hexanes, DMSO, and D2O.
Main Results:
- Carbonyl bond anharmonicity was found to be independent of the solvent environment.
- Simulated 2D IR spectra supported the experimental findings.
- The Stark tuning rate remained unperturbed across different solvent types, including hydrogen and non-hydrogen bonding environments.
Conclusions:
- The vibrational Stark effect is the predominant factor influencing vibrational frequency shifts in carbonyls.
- Carbonyl bond anharmonicity is not significantly affected by solvent polarity or hydrogen bonding.
- Carbonyl probes are reliable for studying intermolecular interactions due to the consistent vibrational Stark effect.
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