Hannover 2013 – scientific programme
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MO: Fachverband Molekülphysik
MO 14: Poster 1: Cluster, Femtosecond Spectroscopy
MO 14.30: Poster
Tuesday, March 19, 2013, 16:00–18:30, Empore Lichthof
Isomer-Selective Double Resonance Spectroscopy: Isolating the Spectral Signatures of H+ · (H2O)7 Isomers — Nadja Heine, •Matias R. Fagiani, Torsten Wende, and Knut R. Asmis — Fritz-Haber-Institut der Max-Planck Gesellschaft, Faradayweg 4-6,14195 Berlin, Germany
Understanding how protons are hydrated remains an important and challenging research area. The anomalously high proton mobility of water can be explained by a periodic isomerization between the Eigen, H3O+(aq), and Zundel, H2O · · H+ · · OH2(aq), binding motifs, even though the detailed mechanism is more complex. These rapidly interconverting structures from the condensed phase can be stabilized, isolated and studied in the gas phase in the form of protonated water clusters. The smallest protonated water clusters that exhibits structural isomers related to the Eigen and Zundel motifs experimentally is the protonated water hexamer H+(H2O)6. For the heptamer, H+(H2O)7, the presence of at least three isomers has been suggested but, due to spectral congestion, these could not be unambiguously assigned. Here, we present results on isomer-selective infrared/infrared (IR/IR) double resonance experiments on H+(H2O)7. Protonated water clusters are formed by electrospray ionization, mass-selected, cooled to cryogenic temperatures and messenger-tagged (H2) in a buffer gas filled ion trap. Isomer-selective IR photodissociation spectra are measured from 2880−3850 cm−1 by population-labeling IR/IR double resonance spectroscopy. Aided by electronic structure calculations four isomers, three Eigen and one Zundel-type isomers, are identified.