1. Kinetics measurements of HO 2 and RO 2 self and cross reactions using infrared kinetic spectroscopy (IRKS) A.C. Noell, L. S. Alconcel, D.J. Robichaud, M. Okumura, S. P. Sander* *Jet Propulsion Laboratory Department of Chemistry, California Institute of Technology Pasadena, CA, USA 62nd International Symposium on Molecular Spectroscopy June 18 th, 2007

2. Urban Air, High NO x Clean Air, low NO x Peroxy Radicals in the Atmosphere The central reaction leading to tropospheric O 3 production Hydroperoxides are radical reservoirs, i.e. they can remove O 3 forming species May be important in secondary organic aerosol formation

3. Reactions of Peroxy Radicals

4. RO 2 self reaction has a radical product branch

5. complicates the kinetics of RO 2 and HO 2 determines the amount of secondary HO 2

6. Secondary HO 2 in the self rxn of C 2 H 5 O 2 Modeled w/ FACSIMILE

7. No previous direct measurements of at atmospheric conditions CH 3 O 2 7 previous studies, T 223 - 573 K, P 50 - 760 Torr C 2 H 5 O 2 3 previous studies, T 298 – 373 K, P 6.5 – 700 Torr i-C 3 H 7 O 2 2 previous studies, T 302, 333, 373 K, P 700 Torr All but one study were based on end product analysis using a variation of GC/MS or FTIR

8. Previous techniques lacked sensitivity and specificity UV absorption was used to monitor both HO 2 and RO 2. SpecificitySensitivity GC/MS and FTIR Unable to detect direct radical products UV Not sensitive enough to detect small amounts of radical product from self reaction

9. Objective: Measure for the C 2 H 5 O 2 (EtO 2 ) self reaction “directly” Simultaneous measurement of and kinetics Use Infrared Kinetic Spectroscopy (IRKS) technique

10. The IRKS method uses NIR spectroscopy to detect HO 2 with high sensitivity a. HO 2 alone is detected by NIR diode laser wavelength modulation spectroscopy b. EtO 2 (or other RO 2 ) is detected by UV absorption, λ = 250 nm, minimizes HO 2 interference 2v 1 Q(9) band is used High sensitivity: Detection limit ~ 5 x 10 11 (molec/cc). Able to detect secondary HO 2 from EtO 2 self rxn. 6638.2 cm -1, 3 ~ 0.05 cm -1 3 DeSain et al. J. Mole Spec 219 (2003) 163–169

11. Experimental Apparatus 6.8 MHz current modulator Demodulated signal Excimer laser, 308 nm D 2 lamp diode laser Mono- chromator computer 2 x Freq, phase shifter FM signal Herriott cell gas entrance exit PD UV NIR InGaAs detector

12. EtO 2 + EtO 2 at 273 K and 50 Torr measured by fitting secondary HO 2

13. is lower than previous measurements = 0.32 ± 0.13 with no T dependence from 221 – 296 K

14. HO 2 + EtO 2 kinetics are sensitive to

15. Comparison of results Self reaction CH 3 O 2 1 Range: 0.28-0.43 573K ~ 0.82 223K ~ 0.10 Only 1 study below 298K EtO 2 2 Range: 0.57- 0.68 373K ~ 0.72 No studies below 298K EtO 2 current 0.32± 0.13No T dep over 221 – 296 K i-C 3 H 7 O 2 2 Range: 0.58 - 0.65 373K = 0.74 1 Tyndall et al. J. Geophys. Res.106 D11 (2001) 12157-12182 2 Lightfoot et al. Atmos. Env. 26 A No 10 (1992) 1805-1961

16. Theory has not provided a simple mechanism for the RO 2 self reaction Russell mechanism 4 Ghigo et al. J. Chem. Phys. 118 No. 23 (2003) 10575-10583 2 R 2 CH-O + O 2 Tetroxide transition state leading to stable products has not been found

17. Summary and Future Work for the EtO 2 self reaction was measured directly by observing the time dependent absorption of HO 2 in the near IR using the IRKS technique The temperature dependence of was measured for the first time over the range 221-296 K for EtO 2 disagrees with the end product studies on the same system Theory does not currently provide a good explanation for the stable product channel that this work measures as the dominant one Investigations of the MeO 2 system

18. References and Acknowledgements Thanks to –Dave Natzic –Lance Christensen –The Okumura and Sander groups NASA Upper Atmosphere Research and Tropospheric Chemistry Programs NASA Graduate Student Researchers Program Fellowship Funding