Hannover 2003 – scientific programme

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MO: Molekülphysik

MO 12: Poster II

MO 12.4: Poster

Thursday, March 27, 2003, 16:00–18:30, Lichthof

IR spectra of C₆H₅⁺-X (X=Ar, N₂, HF) cation complexes — •Otto Dopfer and Nicola Solca — Institut für Physikalische Chemie, Universität Basel, Klingelbergstrasse 80, CH-4056 Basel, Schweiz

The phenyl cation, C₆H₅⁺, is a fundamental intermediate in organic chemical reactions [1]. The present contribution reports IR spectra of C₆H₅⁺-X (X=Ar, N₂, HF) cation complexes recorded in the gas phase. The spectra are obtained by IR photodissociation spectroscopy (IRPD) in a tandem mass spectrometer [2]. The complexes are produced in two different ways: (i) electron impact ionization (EI) of bromobenzene (to produce C₆H₅⁺) followed by three-body association reactions to form C₆H₅⁺-X (X=Ar, N₂), and (ii) chemical ionization (CI) of fluorobenzene using CH₄ to produce C₆H₅⁺-HF [3]. Observation of the asymmetric C-H stretch vibration [1] around 3110 cm⁻¹ unambiguously shows that the phenyl cation is formed by both methods. However, additional transitions are detected for C₆H₅⁺-X (X=Ar, N₂), indicating that either open-chain isomers of C₆H₅⁺ or the ³B₁ triplet state of the phenyl cation are produced by process (i). Besides the C-H stretch vibrations, the H-F stretch of C₆H₅⁺-HF is observed around 3650 cm⁻¹ [4].

[1] M. Winkler and W. Sander, Angew. Chem. Int. Ed. 39 (2000) 2014. [2] E.J. Bieske and O. Dopfer, Chem. Rev. 100 (2000) 3963. [3] J. Hrusak, D. Schroeder, T. Weiske and H. Schwarz, J. Am. Chem. Soc. 115 (1993) 2015. [4] N. Solca and O. Dopfer, J. Am. Chem. Soc., in press.