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Infrared and Near-Infrared Spectroscopy of Acetylacetone and Hexafluoroacetylacetone.

  • Howard DL †Australian Synchrotron, 800 Blackburn Road, Clayton, Victoria 3168, Australia.
  • Kjaergaard HG ‡Department of Chemistry, University of Otago, P.O. Box 56, Dunedin 9016, New Zealand.
  • Huang J ∥Department of Pharmaceutical Science, University of Maryland, Baltimore, Maryland 21201, United States.
  • Meuwly M ⊥Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland.
  • 2015-04-21
Published in:
  • The journal of physical chemistry. A. - 2015
Gases
Hydrocarbons, Fluorinated
Hydrogen Bonding
Molecular Dynamics Simulation
Molecular Structure
Pentanones
Pressure
Protons
Spectrophotometry, Infrared
Spectroscopy, Near-Infrared
Temperature
English The infrared and near-infrared spectra of acetylacetone, acetylacetone-d8, and hexafluoroacetylacetone are characterized from experiment and computations at different levels. In the fundamental region, the intramolecular hydrogen bonded OH-stretching transition is clearly observed as a very broad band with substantial structure and located at significantly lower frequency compared to common OH-stretching frequencies. There is no clear evidence for OH-stretching overtone transitions in the near-infrared region, which is dominated by the CH-stretching overtones of the methine and methyl CH bonds. From molecular dynamics (MD) simulations, with a potential energy surface previously validated for tunneling splittings, the infrared spectra are determined and used in assigning the experimentally measured ones. It is found that the simulated spectrum in the region associated with the proton transfer mode is exquisitely sensitive to the height of the barrier for proton transfer. Comparison of the experimental and the MD simulated spectra establishes that the barrier height is around 2.5 kcal/mol, which favorably compares with 3.2 kcal/mol obtained from high-level electronic structure calculations.
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  • English
Open access status
green
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https://sonar.ch/global/documents/232029
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