title: Isomer-selective detection of hydrogen-bond vibrations in the protonated water hexamer.
abstract: The properties of hydrogen ions in aqueous solution are governed by the ability of water to incorporate ions in a dynamical hydrogen bond network, characterized by a structural variability that has complicated the development of a consistent molecular level description of H(+)(aq). Isolated protonated water clusters, H(+)(H2O)n, serve as finite model systems for H(+)(aq), which are amenable to highly sensitive and selective gas phase spectroscopic techniques. Here, we isolate and assign the infrared (IR) signatures of the Zundel-type and Eigen-type isomers of H(+)(H2O)6, the smallest protonated water cluster for which both of these characteristic binding motifs coexist, down into the terahertz spectral region. We use isomer-selective double-resonance population labeling spectroscopy on messenger-tagged H(+)(H2O)6·H2 complexes from 260 to 3900 cm(-1). Ab initio molecular dynamics calculations qualitatively recover the IR spectra of the two isomers and allow attributing the increased width of IR bands associated with H-bonded moieties to anharmonicities rather than excited state lifetime broadening. Characteristic hydrogen-bond stretching bands are observed below 400 cm(-1).
authors.affiliation: Fritz-Haber-Institut der Max-Planck-Gesellschaft , Faradayweg 4-6,14195 Berlin, Germany.
authors.forename: Nadja
authors.initials: N
authors.lastname: Heine
authors.forename: Matias R
authors.initials: MR
authors.lastname: Fagiani
authors.forename: Mariana
authors.initials: M
authors.lastname: Rossi
authors.forename: Torsten
authors.initials: T
authors.lastname: Wende
authors.forename: Giel
authors.initials: G
authors.lastname: Berden
authors.forename: Volker
authors.initials: V
authors.lastname: Blum
authors.forename: Knut R
authors.initials: KR
authors.lastname: Asmis
mesh_terms: D006860:Hydrogen Bonding; D011522:Protons; D011789:Quantum Theory; D013237:Stereoisomerism; D014732:Vibration; D014867:Water / Q000737:chemistry*
chemical_list: D011522:Protons; D014867:Water