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

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

H C 7 H 6 m/z 90

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

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

PIMS

HC≡CH m/z 26

Supersonic jet of radicals/Ne into 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]  pulse -1  (nozzle)  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

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

Matrix Isolation Spectroscopy of 0.05% Ethylbenzene in Neon

13 C

No m/z 66 !!!

Cycloheptatrienyl Radical ??

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…

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

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

13 C Norobornadienyl

Isotopic Labeling to Help Measured PIMS for:

H/D Scrambling is Facile

13 C Methyl-Phenyl Radical