1. 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

2. 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

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

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

6. 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

7. 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 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

8. 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

9. 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 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

10. 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.

11. 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, % of CH2OO molecules are reacting. We detect only % of the nascent species.
C. C. Womack, M. –A. Martin-Drumel, G. G. Brown, R. W. Field, M. C. McCarthy, Science Advances, 1, e , (2015)

12. 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

13. 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

14. 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

15. 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 × 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠/𝑝𝑢𝑙𝑠𝑒
𝐶𝐻 2 𝑂𝑂+ 𝑂 3 𝑘 𝐶 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠
[ 𝐶𝐻 2 𝑂𝑂 ] 𝑒𝑥𝑝𝑡 =6× 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠/𝑝𝑢𝑙𝑠𝑒
𝐶𝐻 2 𝑂𝑂+ 𝐶𝐻 2 𝑂𝑂 𝑘 𝐷 𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠

16. 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.

17. 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

18. 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