INFRARED SPECTROSCOPY OF M$^+$(CH$_4$)$_n$(H$_2$O)$_{3-4}$ CLUSTERS (M=Li, Na): INDUCING H$_2$O$\cdots$H$_2$O AND H$_2$O$\cdots$CH$_4$ HYDROGEN BONDS IN METHANATED CLUSTERS
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Date
2010
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Ohio State University
Abstract
Experiments on M$^+$(CH$_4$)$_n$(H$_2$O)$_{3-4}$ (M=Li and Na) have been carried out using tandem mass spectrometry and infrared spectroscopy in the O-H stretching region from 3400 cm$^{-1}$ to 3800 cm$^{-1}$. We have found, for example, that a single CH$_4$ can induce hydrogen bonded conformers in the cases of Li$^+$(CH$_4$)$_1$(H$_2$O)$_3$Ar$_{0-1}$, which are absent in the Li$^+$(H$_2$O)$_3$Ar$_{0-1}$ spectra {\textbf{130}}, 15381 (2008).}$^,$ {\textbf{130}}, 15393 (2008).}. Furthermore, upon addition of multiple CH$_4$ ligands, hydrogen bonding is not only maintained, but features associated with H$_2$O$\cdots$CH$_4$ hydrogen bonds are more intense, indicating the affinity of CH$_4$ to bind to available O-H sites. Spectra of Li$^+$(CH$_4$)$_{1-3}$(H$_2$O)$_4$ and Na$^+$(CH$_4$)$_{1-3}$(H$_2$O)$_{3-4}$ clusters will also be discussed, all of which exhibit the curious trait of H$_2$O$\cdots$H$_2$O and H$_2$O$\cdots$CH$_4$ hydrogen bonding in the presence of hydrophobic, non-polar CH$_4$. To better understand the nature and onset of H$_2$O$\cdots$CH$_4$ hydrogen bonding, the Li$^+$(CH$_4$)$_n$(H$_2$O)$_{1-2}$ spectra will be discussed.
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Author Institution: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801