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Title:Infrared absorption of methanol-water clusters mn(h2o), n = 1-4, recorded with the vuv-ionization/ir-depletion techniques
Author(s):Lee, Yu-Fang
Contributor(s):Lee, Yuan-Pern
Abstract:We investigated IR spectra in the CH- and OH-stretching regions of size-selected methanol-water clusters, M$_{n}$(\chem{H_2O}) with M representing \chem{CH_3OH} and {\it n} = 1-4, in a pulsed supersonic jet by using the VUV (vacuum-ultraviolet)-ionization/IR-depletion technique. The VUV light at 118 nm served as the source of ionization in a time-of-flight mass spectrometer. The tunable IR laser served as a source of dissociation for clusters before ionization. Spectra of methanol-water clusters in the OH region show significant variations as the number of methanol molecules increase, whereas spectra in the CH region are similar. For M(\chem{H_2O}), absorption of a structure with \chem{H_2O} as a proton donor was observed at 3570, 3682, and 3722 \wn, whereas that of methanol as a proton donor was observed at 3611 and 3753 \wn. For M$_{2}$(\chem{H_2O}), the OH-stretching band of the dangling OH of \chem{H_2O} was observed at 3721 \wn, whereas overlapped bands near 3425, 3472, and 3536 \wn correspond to the OH-stretching modes of three hydrogen-bonded OH in a cyclic structure. For M$_{3}$(\chem{H_2O}), the dangling OH shifts to 3715 \wn, and the hydrogen-bonded OH-stretching bands become much broader, with a band near 3179 \wn having the smallest wavenumber. Scaled harmonic vibrational wavenumbers and relative IR intensities predicted for the methanol-water clusters with the M06-2X/aug-cc-pVTZ method are consistent with our experimental results. For M$_{4}$(\chem{H_2O}), observed spectrum agree less with theoretical predictions, indicating the presence of isomers other than the most stable cyclic one. Spectra of M$_{n}$(\chem{H_2O}) and M$_{n+1}$ are compared and the cooperative hydrogen-bonding is discussed.
Issue Date:2016-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Rights Information:Copyright 2016 by the authors
Date Available in IDEALS:2017-01-26

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