1. Rate Constant for the Reactions Between OH and Perfluorinated Alkenes
Vladimir L. Orkin, Gregory A. Poskrebyshev, Michael J. Kurylo, J. Phys. Chem. A 115 (2011)
Jeff Joens
CHM 4930
May 26, 2015

2. Chlorofluorocarbons (CFCs) - Halogenated alkanes
- Can be liquified by compression
- Chemically inert
- Relatively inexpensive

3. Environmental Effects Ozone depletion
CFC (troposphere) CFC (stratosphere)
CFC + h Cl + other products
step 1 Cl + O ClO + O2
step 2 ClO + O Cl + O2
net O3 + O O2

4. Environmental Effects Global Warming - Long lifetime in atmosphere
- Strong IR absorber
CFC-12

5. Fluorinated Alkenes (FA)
- Similar properties to CFCs
- Expected to be more reactive in troposphere
- Reaction in troposphere
FA + OH “products”
FA = CF2=CF2
CF2=CFCF3
cis- , trans- CF3CF=CFCF3
(CF3)2C=CFC2H5

6. Flash Photolysis-Resonance Fluorescence

7. Experimental Conditions
Pseudo-first order ( [FA] >> [OH] )
Inlet gas mixture (argon + H2O) + (argon + FA)
OH production H2O + Xe flash OH + H
OH detection resonance fluorescence

8. Pseudo-first Order Kinetics
FA + OH “products”
Rate = kbi [FA] [OH]  k1 [OH] k1 = kbi [FA]0
[FA]0 >> [OH]
[OH] = [OH]0 exp(-k1t)

9. Results

10. Results for CF2=CF2 and CF3CF=CF2

11. Results for cis- ,trans- CF3CF=CFCF3 and
(CF3)2C=CFC2F5

12. Two Reactions?
Low temperature addition (Ea < 0)
High temperature (?) (Ea > 0)

13. Lifetimes in Troposphere
Compound Lifetime
CF2=CF days
CF3CF=CF days
cis-CF3CF=CFCF days
trans-CF3CF=CFCF days
(CF3)2C=CFCF days

14. Future Work
- Extend the range of temperatures
- Product analysis

15. Conclusions
- Low molecular mass FAs are relatively harmless to the environment
- Kinetic questions remain
- Products of OH reaction are not known

16. References
Finlayson-Pitts, B. J., J. N. Pitts, Jr. Chemistry of the Upper and Lower Atmosphere. Academic Press: New York, 2000.
Orkin, V, L., G. A. Poskrebyshev, M. J. Kurylo “Rate Constants for the Reactions Between OH and Perfluorinated Alkenes” J.Phys.Chem.A 115 (2011)
Velders, G. J. M., A. R. Ravishankara, M. K. Miller, M. J. Molina, J. Alcamo, J. S. Daniel, D. W. Fahey, S. A. Montzka, S. Reimann “Preserving Montreal Protocol Climate Benefits by Limiting HFCs” Science 335 (2012)