title: Site-specific vibrational spectral signatures of water molecules in the magic H3O+ (H2O)20 and Cs+ (H2O)20 clusters.
abstract: Theoretical models of proton hydration with tens of water molecules indicate that the excess proton is embedded on the surface of clathrate-like cage structures with one or two water molecules in the interior. The evidence for these structures has been indirect, however, because the experimental spectra in the critical H-bonding region of the OH stretching vibrations have been too diffuse to provide band patterns that distinguish between candidate structures predicted theoretically. Here we exploit the slow cooling afforded by cryogenic ion trapping, along with isotopic substitution, to quench water clusters attached to the H3O(+) and Cs(+) ions into structures that yield well-resolved vibrational bands over the entire 215- to 3,800-cm(-1) range. The magic H3O(+)(H2O)20 cluster yields particularly clear spectral signatures that can, with the aid of ab initio predictions, be traced to specific classes of network sites in the predicted pentagonal dodecahedron H-bonded cage with the hydronium ion residing on the surface.
authors.affiliation: Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, CT 06520;
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Fournier
authors.affiliation: Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, CT 06520;
authors.forename: Conrad T
authors.initials: CT
authors.lastname: Wolke
authors.affiliation: Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, CT 06520;
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Johnson
authors.affiliation: Sterling Chemistry Laboratory, Department of Chemistry, Yale University, New Haven, CT 06520; mark.johnson@yale.edu knut.asmis@uni-leipzig.de.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Johnson
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany; and.
authors.forename: Nadja
authors.initials: N
authors.lastname: Heine
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany; and.
authors.forename: Sandy
authors.initials: S
authors.lastname: Gewinner
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany; and.
authors.forename: Wieland
authors.initials: W
authors.lastname: Schöllkopf
authors.affiliation: Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, D-04103 Leipzig, Germany.
authors.forename: Tim K
authors.initials: TK
authors.lastname: Esser
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany; and Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, D-04103 Leipzig, Germany.
authors.forename: Matias R
authors.initials: MR
authors.lastname: Fagiani
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany; and Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, D-04103 Leipzig, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Knorke
authors.affiliation: Wilhelm-Ostwald-Institut für Physikalische und Theoretische Chemie, Universität Leipzig, D-04103 Leipzig, Germany mark.johnson@yale.edu knut.asmis@uni-leipzig.de.
authors.forename: Knut R
authors.initials: KR
authors.lastname: Asmis
keywords: cryogenic vibrational spectroscopy; hydrogen bonding; water clusters