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 Title: Isomer-specific IR2MS2 spectroscopy of protonated water clusters Author(s): Asmis, Knut R. Subject(s): Mini-symposium: Beyond the Mass-to-Charge Ratio: Spectroscopic Probes of the Structures of Ions Abstract: Understanding how protons are hydrated remains an important and challenging research area. The anomalously high proton mobility of water, for example, can be explained by a periodic isomerization between the Eigen and Zundel binding motifs, H$_{3}$O$^{+}$(\emph{aq}) and H$_{5}$O$_{2}$$^{+}(\emph{aq}), respectively, even though the detailed mechanism is considerably more complex and not completely understood. These rapidly interconverting structures from the condensed phase can be stabilized, isolated and studied in the gas phase in the form of protonated water clusters. Infrared photodissociation (IRPD) spectroscopy serves as a powerful tool for studying the structure of gas phase clusters. However, the contribution of multiple isomers to the IRPD spectrum can complicate the assignment. Here, results on the isomer-specific IR/IR double resonance (IR^{2}MS^{2}) spectroscopy of the protonated water clusters H^{+}(H_{2}O)_{\emph{n}}$$\cdot$H$_{2}$ with \emph{n} = 5-10 are reported. IR$^{2}$MS$^{2}$ spectra are measured in the spectral region of the free and hydrogen-bonded OH-stretching vibrations (2880-3850 \wn) and assigned on the basis of a comparison to the results of electronic structure calculations. For the protonated water hexamer, it is demonstrated that combining the radiation from an IR free electron laser with that from a widely tunable table-top IR laser allows extending this technique across nearly the complete IR region (260-3900 \wn). \emph{Ab initio} molecular dynamics calculations qualitatively recover the IR spectra of the two isomers for \emph{n} = 6 and allow identifying characteristic hydrogen-bond stretching bands below 400 \wn. Issue Date: 2014-06-19 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Asmis, K.R. ISOMER-SPECIFIC IR2MS2 SPECTROSCOPY OF PROTONATED WATER CLUSTERS. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.RG01 Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/59152 DOI: 10.15278/isms.2014.RG01 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-12-082015-04-14
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