International Symposium on Molecular Spectroscopy// June 26, 2015 Observation of the simplest Criegee intermediate (CH2OO) in the gas phase ozonolysis of ethylene Carrie Womack, Marie-Aline Martin-Drumel, Gordon Brown, Robert Field, Michael McCarthy Massachusetts Institute of Technology, Harvard-Smithsonian Center for Astrophysics, Coker College International Symposium on Molecular Spectroscopy// June 26, 2015

Understanding oxidation chemistry is key to modeling the troposphere OH/O3/hv VOCs (alkenes, other hydrocarbons), NOX, SOX Oxidized VOCs Secondary organic aerosol (SOA) Cloud formation

Ozonolysis is a major mechanism for alkene oxidation in the troposphere “primary ozonide” “Criegee intermediate” Unimolecular isomerization and dissociation Stabilization Bimolecular reaction

Criegee intermediates are currently receiving a lot of attention hν CH2I2 CH2I CH2OO Improved method developed R. Criegee postulates mechanism First laboratory detection of CH2OO

The photolysis method has a few drawbacks O3 + C2H4 O3 + C3H6 O3 + isoprene 1) Larger Criegee intermediates will require larger diiodo-substituted precursors 2) Branching ratios of the overall ozonolysis reaction are not measured

The detection of CH2OO in ethylene ozonolysis will require: 1) High reactant concentration React at room pressure and temperature with high concentration Because kform = 1.45 x 10-18 cm3 molecule-1 sec-1 2) Sensitive detection Cavity Fourier transform microwave spectroscopy Stabilization Unimolecular isomerization and dissociation To detect species with ~ppb concentration Bimolecular reaction 3) Rapid sampling Customized nozzle for fast sampling To minimize secondary chemistry

Cavity Fourier transform microwave spectroscopy is a highly selective and precise detection method Peak assignments are nearly unique Many different species can be measured in quick succession Peak intensity is directly proportional to molecular abundance in the gas pulse

The detection of CH2OO in ethylene ozonolysis will require: 1) High reactant concentration React at room pressure and temperature with high concentration Because kform = 1.45 x 10-18 cm3 molecule-1 sec-1 2) Sensitive detection Cavity Fourier transform microwave spectroscopy To detect species with ~ppb concentration 3) Rapid sampling Customized nozzle for fast sampling To minimize secondary chemistry

A modified pulsed nozzle acts as a fast flow reactor See J. Z. Gillies, C. W. Gillies, F. J. Lovas, R. Suenram, E. Kraka, D. Cremer, JACS, 1991, 113, 6408.

The fundamental 10,1-00,0 line of CH2OO was observed The peak assignment was confirmed by double resonance. The signal was also dependent on both reactants. The peak intensity indicates ~6 x 109 molecules/pulse (~6 x 1011 molecules/cm3, or ~1 ppb). Given reactant concentrations, 99.99992% of CH2OO molecules are reacting. We detect only 0.00008% of the nascent species. C. C. Womack, M. –A. Martin-Drumel, G. G. Brown, R. W. Field, M. C. McCarthy, Science Advances, 1, e1400105, (2015)

Rotational Transition Absolute abundance (molecules/pulse) Secondary Criegee chemistry is also evident Molecule Rotational Transition Frequency (MHz) Absolute abundance (molecules/pulse) Relative abundance CH2OO 10,1-00,0 23,186.49 6 x 109 1 van der Waals complex 21,1-10,1 15,800.78 3 x 1012 500 Formaldehyde 21,2-21,1 14,488.48 2 x 1016 3.3 x 106 Dioxirane 21,1-20,2 31,752.88 3 x 1011 50 Formic acid 22,471.18 2 x 1013 3333 Ethylene ozonide 11,1-00,0 12,828.62 5 x 1011 83 Ethylene oxide 11,0-10,1 11,385.91 8 x 1011 133 Acetaldehyde 21,2-11,1 8,243.47 7 x 1012 1166 Formic anhydride 11,734.13 2 x 1012 333

Unimolecular reactions: Molecule Relative abundance CH2OO 1 van der Waals complex 500 Formaldehyde 3.3 x 106 Dioxirane 50 Formic acid 3333 Ethylene ozonide 83 Ethylene oxide 133 Acetaldehyde 1166 Formic anhydride 333 observed couldn’t look for

Bimolecular reactions: Stabilization Molecule Relative abundance CH2OO 1 van der Waals complex 500 Formaldehyde 3.3 x 106 Dioxirane 50 Formic acid 3333 Ethylene ozonide 83 Ethylene oxide 133 Acetaldehyde 1166 Formic anhydride 333 observed couldn’t look for

A simple kinetic model agrees with our experimental CH2OO abundances 𝑂 3 + 𝐶 2 𝐻 4 𝑘 𝑓𝑜𝑟𝑚 𝐶𝐻 2 𝑂𝑂+ 𝐶𝐻 2 𝑂 𝑑[ 𝐶𝐻 2 𝑂𝑂] 𝑑𝑡 ≈0= 𝑘 𝑓𝑜𝑟𝑚 𝑂 3 𝐶 2 𝐻 4 − 𝑘 𝑢𝑛𝑖 𝐶𝐻 2 𝑂𝑂 − 𝑘 𝐴 𝐶 𝐻 2 𝑂𝑂 𝐶𝐻 2 𝑂 − 𝑘 𝐵 𝐶 𝐻 2 𝑂𝑂 𝐶 2 𝐻 4 − 𝑘 𝐶 𝐶𝐻 2 𝑂𝑂 𝑂 3 − 𝑘 𝐷 [ 𝐶𝐻 2 𝑂𝑂] 2 𝐶 𝐻 2 𝑂𝑂 𝑘 𝑢𝑛𝑖 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝐶𝐻 2 𝑂𝑂+𝐶 𝐻 2 𝑂 𝑘 𝐴 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 𝐶𝐻 2 𝑂𝑂+ 𝐶 2 𝐻 4 𝑘 𝐵 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 [ 𝐶𝐻 2 𝑂𝑂 ] 𝑚𝑜𝑑𝑒𝑙 = 3±1 × 10 9 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠/𝑝𝑢𝑙𝑠𝑒 𝐶𝐻 2 𝑂𝑂+ 𝑂 3 𝑘 𝐶 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 [ 𝐶𝐻 2 𝑂𝑂 ] 𝑒𝑥𝑝𝑡 =6× 10 9 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠/𝑝𝑢𝑙𝑠𝑒 𝐶𝐻 2 𝑂𝑂+ 𝐶𝐻 2 𝑂𝑂 𝑘 𝐷 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

Conclusions and future directions Using cavity FTMW spectroscopy and a modified pulsed nozzle, we have measured CH2OO in the gas phase ozonolysis of ethylene for the first time. The abundances of the other species in the O3 + C2H4 reaction qualitatively agree with the literature values. With improvements to the experimental design, we hope larger O3 + alkene systems can be explored.

Acknowledgements McCarthy group (Harvard-Smithsonian Center for Astrophysics) Dr. Mike McCarthy Dr. Marie-Aline Martin-Drumel, Prof. Gordon Brown (Coker College), Prof. Kyle Crabtree, Dr. Oscar Martinez, Sam Palmer, Paul Antonnuci, Dr. Carl Gottlieb Field group (Massachusetts Institute of Technology) Prof. Bob Field Dr. Barratt Park, David Grimes, Jun Jiang, Tim Barnum, Alex Hull, Trevor Erickson, Ethan Klein, Catherine Saladrigas, Alice Green Funding National Science Foundation, Department of Energy, The Camille and Henry Dreyfus Foundation

Microwave (rotational) spectroscopy gives geometries (chemwiki.ucdavis.edu) Measure rotational transitions 𝐸 𝐽 𝐾 𝑎 , 𝐾 𝑐 =[𝐶𝑂𝑀𝑃𝐿𝐼𝐶𝐴𝑇𝐸𝐷] 𝐸 𝐽 =𝐵𝐽 𝐽+1 𝑤ℎ𝑒𝑟𝑒 𝐵= ℏ 2 2𝐼 𝑎𝑛𝑑 𝐼= 𝑚 𝑖 𝑟 𝑖 2 𝐴= ℏ 2 2 𝐼 𝐴 , 𝐵= ℏ 2 2 𝐼 𝐵 , 𝐶= ℏ 2 2 𝐼 𝐶 ∆ 𝐸 𝐽+1←𝐽 =2𝐵(𝐽+1) Derive B Calculate bond lengths