1. MOTIVATIONS : Atmospheric Chemistry Troposphere Chemistry – Ozone Production RO 2 + NO → RO + NO 2 NO 2 → NO + O( 3 P) O( 3 P) + O 2 + M → O 3 + M

2. M. J. Pilling, Comprehensive Chemical Kinetics, 35, 1(1997) MOTIVATIONS : Low Temperature Combustion

3. Cavity Ringdown Absorption Spectroscopy Time Intensity 00  absorber cL)/( 0  R1   (a) (b)  ln    cL)/( R1  L=1m R=0.99%  0 =34  s A = n  l L eff =10 km Sensitive R L A = L/c  absorber - L/c  0

4. Experimental Setup Ringdown Cell YAG 532 nmSirah Dye Laser H 2 Raman Cell PD High Reflectivity Mirrors ArF 193 nm 650 – 700 mJ90 – 130 mJ 1 – 2 mJ 160 – 200 mJ 1.5 - 1.1  m 2 nd Stokes Filters DCM & Rhodamine B/101 580 – 640 nm

5. Origin of the A 2 A - X 2 A Electronic Transition of CH 3 O 2 Reaction* Initiation: Precursor + hν  R+(CO, Br, I, CO 2 ) Production: O 2 +R+M  RO 2 +M Radical-Radical Losses: R+R+M  R 2 +M R+RO 2  2RO RO 2 +RO 2  Products *precursor for CH 3 - acetone / methyl iodide

6. 0-0 cm -1 Origin of the A 2 A - X 2 A Electronic Transition of CH 3 O 2 ~ / M. B. Pushkarsky, S. J. Zalyubovsky, and T. A. Miller, J. Chem. Phys. 112, 10695 (2000)

7. MOTIVATIONS : Why C 6 H 5 O 2 and How ? The reaction of phenyl radical (C 6 H 5 ) with molecular oxygen is postulated to impede the formation of soot inherent in hydrocarbon combustion, according to the following mechanism. O2O2 C6H5O2C6H5O2

8. Production of C 6 H 5 radical from Acetophenone at 193 nm 3 Channels C 6 H 5 COCH 3 + hv  C 6 H 5 + CH 3 CO (2) C 6 H 5 CH 3 + CO (3) C 6 H 5 CO + CH 3 (1) C 6 H 5 COCH 3 + hv  (1) and (2) have comparable cross sections. Cross section for channel (3) is estimate to be less than 0.1 % of those processes (1) and (2). 30 – 50 % of primary C 6 H 5 CO further decomposes, yielding secondary products C 6 H 5 + CO and CH 3 + CO respectively Zhao, H.-Q. et al. Journal of Chemical Physics (1997), 107(18), 7230-7241.

9. Photolysis of acetophenone at 193 nm Bond Origin Acetophenone at 193 nm (1) Acetone at 193 nm (1) M. B. Pushkarsky, S. J. Zalyubovsky, and T. A. Miller, J. Chem. Phys. 112, 10695 (2000)

10. Comparaison with other precursors Acetophenone at 193 nm (1) Acetone at 193 nm Bromobenzene at 193 nm PhO 2 MeO 2

11. Photolysis of acetophenone at 193 nm Band Origin MeO 2 PhO 2

12. Photolysis of acetophenone at 193 nm O-O Stretch PhO 2 MeO 2

13. Tentative assignment O-O stretch 14 0 1 12 0 1

14. Tentative assignment 23 0 1

15. Tentative assignment Zoom 000000 33 1 1 33 2 2 33 3 3

16. Assignment 33 0 1

17. Conclusion and Future Work ~ ~ We have observed the A 2 A' –X 2 A" electronic transition of phenyl peroxy radical. Assignment has been done. Studying other unsaturated peroxy radicals and other peroxy radicals (C 5 H 11 O 2 ). ~ ~