Spectroscopic identification of ethanol-water conformers by large-amplitude hydrogen bond librational modes

Jonas Andersen, J. Heimdal, René Wugt Larsen

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Abstract

The far-infrared absorption spectra have been recorded for hydrogen-bonded complexes of water with ethanol embedded in cryogenic neon matrices at 2.8 K. The partial isotopic H/D-substitution of the ethanol subunit enabled by a dual inlet deposition procedure enables the observation and unambiguous assignment of the intermolecular high-frequency out-of-plane and the low-frequency in-plane donor OH librational modes for two different conformations of the mixed binary ethanol/water complex. The resolved donor OH librational bands confirm directly previous experimental evidence that ethanol acts as the O⋯HO hydrogen bond acceptor in the two most stable conformations. In the most stable conformation, the water subunit forces the ethanol molecule into its less stable gauche configuration upon dimerization owing to a cooperative secondary weak O⋯HC hydrogen bondinteraction evidenced by a significantly blue-shift of the low-frequency in-plane donor OH librational band origin. The strong correlation between the low-frequency in-plane donor OH librational motion and the secondary intermolecular O⋯HC hydrogen bond is demonstrated by electronic structure calculations. The experimental findings are further supported by CCSD(T)-F12/aug-cc-pVQZ calculations of the conformationalenergy differences together with second-order vibrational perturbation theory calculations of the large-amplitude donor OH librational band origins.
Original languageEnglish
Article number224315
JournalJournal of Chemical Physics
Volume143
Issue number22
Number of pages10
ISSN0021-9606
DOIs
Publication statusPublished - 2015

Keywords

  • Ethanol
  • Hydrogen bonding
  • Molecular conformation
  • Intermolecular forces
  • Absorption spectra

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