title: A combined Raman- and infrared jet study of mixed methanol-water and ethanol-water clusters.
abstract: The vibrational dynamics of vacuum-isolated hydrogen-bonded complexes between water and the two simplest alcohols is characterized at low temperatures by Raman and FTIR spectroscopy. Conformational preferences during adaptive aggregation, relative donor/acceptor strengths, weak secondary hydrogen bonding, tunneling processes in acceptor lone pair switching, and thermodynamic anomalies are elucidated. The ground state tunneling splitting of the methanol-water dimer is predicted to be larger than 2.5 cm(-1). Two types of alcohol-water trimers are identified from the spectra. It is shown that methanol and ethanol are better hydrogen bond donors than water, but even more so better hydrogen bond acceptors. As a consequence, hydrogen bond induced red shifts of OH modes behave non-linearly as a function of composition and the resulting cluster excess quantities correspond nicely to bulk excess enthalpies at room temperature. The effects of weak C-H···O hydrogen bonds are quantified in the case of mixed ethanol-water dimers.
authors.affiliation: Institut für Physikalische Chemie, Universität Göttingen, Tammannstr. 6, 37077 Göttingen, Germany.
authors.forename: Marija
authors.initials: M
authors.lastname: Nedić
authors.forename: Tobias N
authors.initials: TN
authors.lastname: Wassermann
authors.forename: René Wugt
authors.initials: RW
authors.lastname: Larsen
authors.forename: Martin A
authors.initials: MA
authors.lastname: Suhm
mesh_terms: D000431:Ethanol / Q000737:chemistry*; D006860:Hydrogen Bonding; D000432:Methanol / Q000737:chemistry*; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D014867:Water; D000431:Ethanol; D000432:Methanol