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Originally published in Science Express on 30 June 2005
Science 19 August 2005:
Vol. 309. no. 5738, pp. 1219 - 1222
DOI: 10.1126/science.1113729
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Reports

Understanding the Infrared Spectrum of Bare CH5+

Oskar Asvany,1* Padma Kumar P,2* Britta Redlich,3 Ilka Hegemann,2 Stephan Schlemmer,1,4 Dominik Marx2{dagger}

Protonated methane, CH5+, continues to elude definitive structural assignment, as large-amplitude vibrations and hydrogen scrambling challenge both theory and experiment. Here, the infrared spectrum of bare CH5+ is presented, as detected by reaction with carbon dioxide gas after resonant excitation by the free electron laser at the FELIX facility in the Netherlands. Comparison of the experimental spectrum at ~110 kelvin to finite-temperature infrared spectra, calculated by ab initio molecular dynamics, supports fluxionality of bare CH5+ under experimental conditions and provides a dynamical mechanism for exchange of hydrogens between CH3 tripod positions and the three-center bonded H2 moiety, which eventually leads to full hydrogen scrambling. The possibility of artificially freezing out scrambling and internal rotation in the simulations allowed assignment of the infrared spectrum despite this pronounced fluxionality.

1 Leiden Observatory, 2300 RA Leiden, Netherlands.
2 Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany.
3 FELIX Facility, Foundation for Fundamental Research on Matter (FOM) Institute for Plasma Physics "Rijnhuizen," 3430 BE Nieuwegein, Netherlands.
4 I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany.

* These authors contributed equally to this work.

{dagger} To whom correspondence should be addressed. E-mail: dominik.marx{at}theochem.rub.de

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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