Frankfurt 2006 – wissenschaftliches Programm
Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe
MO: Molekülphysik
MO 15: Molecular Clusters II
MO 15.5: Vortrag
Montag, 13. März 2006, 17:30–17:45, H10
Mass-selected Gas Phase Infrared Spectroscopy of NH4+(NH3)n (n=0–7) — •Gabriele Santambrogio1, Mathias Brümmer1, Sara Fontanella1, Yonggang Yang2, Oliver Kühn2, and Knut R. Asmis3 — 1Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany — 2Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany — 3Fritz-Haber-Institut der Max-Planck-Gesellschaft, Abteilung Molekülphysik, Faradayweg 4-6, 14195 Berlin, Germany
The hydrogen bond interaction is key in understanding
the structure and properties of water and biomolecules.
However, our understanding of strong, low-barrier hydrogen bonds and their
central role in enzyme catalysis, biomolecular recognition, proton
transfer across biomembranes and proton transport in aqueous media
remains sketchy.
Here we present results on the infrared photodissociation
spectroscopy of gas phase mass selected NH4+(NH3)n
(n=0–7) in the region between 600 and 2000 cm−1.
The ammonia umbrella mode is observed at 1300 cm−1
for n=1 and is monotonically red-shifted down to 1100 −1 for
n=7. Its position is a measure for the strength of the hydrogen
bonds and shows evidence for closing of the first solvation
shell after n=4. The threefold degenerate antisymmteric stretch mode
of the ammonium ion is observed around 1500 cm-1. Its degenracy is
lifted upon solvation until a symmetric solvation shell is reached
for n=4. Only the n=1 cluster is predicted to exhibit strong
hydrogen bonding and evidence or a shared proton mode is found at
750 cm−1 for n=1. Surprisingly, we also find such spectral
signatures for some of the larger cluster ions.