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Spectroscopic and Kinetic Studies of Atmospheric Free Radicals

Spectroscopic and Kinetic Studies of Atmospheric Free Radicals. Elizabeth Foreman , YiTien Jou , Kara Kapnas , and Craig Murray Department of Chemistry, University of California, Irvine. Reaction of interest: CH 2 I+O 2. CH 2 I + I. CH 2 IOO*. CH 2 I 2 + h ν. CH 2 I + I*. CH 2 + I 2.

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Spectroscopic and Kinetic Studies of Atmospheric Free Radicals

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  1. Spectroscopic and Kinetic Studies of Atmospheric Free Radicals Elizabeth Foreman, YiTienJou, Kara Kapnas, and Craig Murray Department of Chemistry, University of California, Irvine

  2. Reaction of interest: CH2I+O2 CH2I + I CH2IOO* CH2I2 + hν CH2I + I* CH2 + I2 CH2OO + I CH2I + O2 CH2O + IO M=N2 CH2IOO CH2O +IO (low P) + I CH2IO + IO CH2O + IO + I Lee et al. Chem. Eur. J. 2012, 18, 12411-12423.

  3. Kinetic Evidence: CH2IOO CH2OO Spectroscopic Evidence: Sehestedet al. Int. J. Chem. Kinet. 1994, 26, 259 272. Gravestocket al. Chem. Phys. Chem. 2010, 11, 1416-1424. Sheps , L. J. Phys.Chem. Lett. 2013, 4, 4201-4205. Beames et al. J. Am. Chem. Soc. 2012, 49, 20045-20048.

  4. Technique: Cavity Ring-down Spectroscopy PMT Signal

  5. IO Formation Kinetics Absorption spectrum of the precursor molecule CH2I2 Absorption spectrum of the A2Π3/2←X2Π3/2(3,0) band of the IO radical Sander, S. P., J. Abbatt, J. R. Barker, J. B. Burkholder, R. R. Friedl, D. M. Golden, R. E. Huie, C. E. Kolb, M. J. Kurylo, G. K. Moortgat, V. L. Orkin and P. H. Wine, JPL Publication 10-6, Jet Propulsion Laboratory, Pasadena, 2011 http://jpldataeval.jpl.nasa.gov

  6. High O2 Low O2 Pseudo 1st order dependence of IO formation rate on O2 number density kform=4.3±0.8 x 10-14 cm3 molecules-1 s-1 Formation and decay of IO absorption at 30 torr

  7. Consider early times: kform=1.38±0.03 x 10-13 cm3 molecule-1 s-1 Slow rise: secondary reactions kN2=4.9 x 10-31 cm6 molecule-2 s-1 [N2]=8 x 1017 molecules cm-3 Fast rise: direct production k=10-12 cm3 molecule-1 s-1 Huang et al. J. Phys. Chem. Lett. 2012, 3, 3399-3403. Enamiet al. Bull. Chem. Soc. Jpn. 2008, 81, 1250-1257. Eskolaet al. Phys. Chem. Chem. Phys. 2006, 8, 1416-1424. Masaki et al. J. Phys. Chem. 1995, 99, 13126-13131.

  8. I2 Production I2 formation: CH2I2 + hν → CH2 + I2λ<333 nm I+I+M → I2+M Non-photolytic I atom formation: CH2I + O2 →CH2IOO*→CH2OO + I CH2I + O2 →CH2OO + I 28% enhancement in I2 formation in the presence of O2 56% yield (lower limit) for Criegee Intermediate? Absorption spectrum of I2 at 5 torr total pressure

  9. Conclusions and Future Studies • Simple pseudo first order kinetics are insufficient to fully describe IO formation • Formation of IO radical occurs biexponentially • Development of comprehensive kinetic model for CH2I + O2 reaction • Kinetic dependence on O2 number density

  10. Acknowledgements Undergraduates: Craig Murray Ben Toulson Kara Kapnas YiTienJou

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