Helium Nanodroplet Infrared Spectroscopy of the Tropyl Radical RUHR-UNIVERSITÄT BOCHUM FAKULTÄT FÜR CHEMIE UND BIOCHEMIE Lehrstuhl für Physikalische Chemie II Matin Kaufmann

Motivation The Tropyl Radical Reaction intermediate for the formation of PAHs (polycyclic aromatic hydrocarbons) -Organic chemistry and synthesis 1 -Combustion reactions and soot formation 2 -The interstellar mid-IR spectrum suggests presence of PAHs in outer space 3 Cycloheptatrienyl (Tropyl): C 7 H 7 ∙ [1] C. Chatgilialoglu, A. Studer; John Wiley & Sons: Chichester 2012 [2] D. Trogolo et al.; J. Phys. Chem. A 2014, 118, 427 [3] L. J. Allamandola et al.; Astrophys. J., Suppl. Ser. 1989, 71, 733

Motivation C 7 H 7 Isomers Tropyl Benzyl X (-16.8 kcal/mol) 1 [1] R. G. Satink et al.; J. Am. Chem. Soc. 2003, 125, 15714

Previous Work Spectroscopy of Tropyl

Previous Work Electronic State Degeneracy of Tropyl I. Sioutis et al.; J. Chem. Phys. 2008, 128, 84311

Previous Work Experimental Data from LIF Spectroscopy

Experimental Setup Helium Droplet Machine pick-up cells Rough Pump Gate Valve AirVacuum O-ring seal Water cooled copper electrodes Ta filament / Quartz tube Sample

Pyrolysis of Bitropyl Mass Spectra +

Experimental Data IR Spectrum Bitropyl IR Intensity Depletion

Experimental Data IR Spectrum Tropyl IR Intensity Depletion

Jahn-Teller Effect Symmetry Considerations CH stretch vibrations: IR active Electronic ground state: Vanishing Integral Rule: Vibronic coupling: Check of IR activity: → Vibronic Coupling generates a splitting into two 2-fold degenerate transitions

Experimental Data Mass Spectra Comparison

Experimental Data IR Spectrum Comparison Depletion

Conclusion T. Koenig, J. C. Chan; J. Am. Chem. Soc. 1978, 100, 2240

Acknowledgements Douberly Lab at the University of Georgia: Gary Doublery, Bernadette Broderick, Chris Moradi, Joe Brice, Alaina Brown and Peter Franke Havenith Lab at the Ruhr-Universität Bochum: Martina Havenith, Gerhard Schwaab, Theo Fischer, Devendra Mani, Daniel Leicht, Raffael Schwan