1. Thermal Decomposition of Benzyl Radical via Multiple Active Pathways Grant Buckingham, Thomas Ormond, David Robichaud, Patrick Hemberger Mark Nimlos, John Daily, Barney Ellison June 17 th 2014 International Symposium on Molecular Spectroscopy Champaign-Urbana, Illinois

2. Pyrolysis of Benzyl Radical Appearance in combustion of toluene (15% of gasoline) and many bigger molecules e.g. biomass Resonance stabilized, no decomposition till 1300 K Shock tube experiments on benzyl pyrolysis show –Stable final products C 2 H 2 and C 4 H 4 –Production of H atoms Ties in to active field of C 7 H 6 and C 7 H 5 electronic structure calculations … fulvenallene and fulvenallenyl are molecules of interest

3. H C 7 H 6 m/z 90

4. Pyrolysis with a  icrotubular Reactor  Short residence time (  ≈ 25-150 µsec)  Dilute: unimolecular chemistry  Expand to high-vacuum, reactions quenched  Directly identify all atoms, radicals, and metastables 4 1 mm x 3 cm linguini

5. λ=118.2 nm (10.487 eV) Ions to MCP Detector Pulsed Valve & Reactor Assembly PIMS Experimental Set-Up 10 -6 Torr 10 -7 Torr Dilute target molecule in He carrier gas (PhotoIonization Mass Spectrometry)

6. PIMS

8. HC≡CH m/z 26

9. Supersonic jet of radicals/Ne into 10 -6 Torr 5 K CsI window 3 cm downstream 3n-6 vibrational modes per molecule give detailed molecular fingerprint (48 for Ethylbenzene)~~~~~lots of congestion Matrix isolation spectroscopy to corroborate PIMS [radicals]  10 13 pulse -1  (nozzle)  50-200 µsec pyrolysis Products and unstable radical intermediates 0.5 Torr C 6 H 5 CH 2 CH 3 in 1 atm Ne carrier gas After deposition, the window is rotated into the path of a commercial FTIR

10. Matrix Isolation IR Spectroscopy Ethylbenzene  benzyl radical pyrolysis observed in a 5 K neon matrix –Benzyl radical and methyl radical detected at 1300 K –Fulvenallene also at 1400 K –Acetylene and cyclopentadienyl radical detected at 1400 K (mechanism unclear) –Propargyl radical (HCCCH 2 ) detected at 1500 K + + Fulvenallene

11. Matrix Isolation Spectroscopy of 0.05% Ethylbenzene in Neon

12. 13 C

13. No m/z 66 !!!

14. Cycloheptatrienyl Radical ??

15. Tunable Ionization Source Signal ✔ ✔ ✔ ✔ ✗ ✗ m/z 93 IE = 6.22 eV m/z 93 IE = 7.25 eV No cyc-C 7 H 7 Detected…

16. Results & Conclusions Benzyl radical produced in pyrolysis microreactor –Confirmed with photoionization mass spectrometry and matrix isolation IR spectroscopy Presence of fulvenallene corroborated Early decomposition to acetylene (HCCH) and cyclopentadienyl radical (C 5 H 5 ) identified Isotope labeling indicates that a completely new chemical mechanism is required

17. Thanks for your Attention!  National Renewable Energy Laboratory David Robichaud Mark Nimlos  University of Colorado Boulder Tom Ormond Kimberly Urness Jessie Porterfield G. Barney Ellison

20. 13 C Norobornadienyl

21. Isotopic Labeling to Help Measured PIMS for:

23. H/D Scrambling is Facile

24. 13 C Methyl-Phenyl Radical