1. Neal Kline, Meng Huang, and Terry A. Miller Department of Chemistry and Biochemistry The Ohio State University

2. First proposed by Rudolf Criegee in 1949 as intermediate in ozonolysis of alkenes. Formed in the atmosphere and utilized heavily in organic chemistry to functionalize double bonds. Large amounts of research have been focused on the Criegee intermediate recently.

3. 1 A’ 3 A’ 1A11A1 3A23A2 a. Harding, L. B. and Goddard III, W. A. J. Am. Chem. Soc. 1978, 100, 7180-7188. b. Wadt, W. R. and Goddard III, W. A. J. Am. Chem. Soc. 1975, 97, 3004-3021. C=1s 2 2s 2 2p 2 O=1s 2 2s 2 2p 4 9530 cm -1

4. Sirah dye laser 570-705 nm Nd:YAG: 532 nm Raman cell (H 2, 300 psi) 2 nd Stokes: 6000-9000 cm -1 20 Hz ~600 mJ/pulse ~70-80 mJ/pulse ~1-2 mJ/pulse Photolysis: Excimer Laser KrF, 248 nm Highly Reflective Mirror (99.995 %) Highly Reflective Mirror (99.995 %)

5. Photolyze diiodomethane at 248 nm, one iodine atom dissociates. CH 2 I radical reacts with oxygen to give CH 2 IOO. CH 2 IOO then dissociates I atom to give CH 2 OO. a We observed our spectrum under conditions of 86.0 torr total pressure (84.9 torr N 2, 0.1 torr CH 2 I 2, 1.0 torr O 2 ),which is the same conditions as Y. P. Lee. b a.Oliver Welz et al., Science, 335 204, 2012; b. Su, Y.; Huang, Y.; Witek, H. A. and Lee, Y. P. Science 2013, 340, 174.

6. H 2 O Contamination Iodine atom 2 P 1/2  2 P 3/2 Precursor Absorption Precursor Absorption 875 cm -1, Typical OO Stretch Frequency Experimental Spectrum

7. Comparison of the Spectra for CH 2 XOO Radicals 6908 cm -1 6817 cm -1 6799 cm -1 7383 cm -1 Good electronic structure calculations – FD07,Dawes Vibrational spectral analysis– FD06 Wavenumber(cm -1 )

8. a. Huang, H.; Eskola, A.; Taatjes, C. A. J. Phys. Chem. Lett. 2012, 3, 3399. Mechanism requires libration of I upon reaction of CH 2 I+O 2. Photolysis of CH 2 I 2 with O 2 present shows a nearly 50% increase in I atom signal compared to the photolysis without O 2

9. SO 2 is effective Criegee intermediate scavenger and reacts very quickly a,b,c, however reacts very slowly with peroxy radicals d,e. a. D. Stone, M. Blitz, L. Daubney, T. Ingham, and P. Seakins. Phys. Chem. Chem. Phys., 2013,15, 19119-19124. b. L. Sheps. J. Phys. Chem. Lett., 2013, 4, 4201-4205. c. O. Welz, J. D. Savee, D. L. Osborn, S. S. Vasu, C. J. Percival, D. E. Shallcross, and C. A. Taatjes. Science, 2012, 335, 204-207. d. P. D. Lightfoot, R. A. Cox, J. N. Crowley, M. Destriau, G. D. Hayman, M. E. Jenkin, M. J. Rossi, and J. Troe. Atmos. Chem. Phys., 2006, 6, 3625-4055. e. C. S. Kan, J. G. Calvert, and J. H. Shaw. J. Phys. Chem., 1981,85, 1126-1132. 3.9 x 10 -11 cm 3 molec -1 s -1 ≤1 x 10 -16 cm 3 molec -1 s -1

10. Experimental Spectrum of CH 2 ClOO with SO 2

11. Experimental Spectrum of CH 2 BrOO with SO 2

12. Experimental Spectrum of the Carrier Generated by CH 2 I 2 /O 2 mixed with SO 2 Self Reaction? Reaction Mechanism? +SO 2 CH 2 IO 2 + CH 2 IO 2 → 2CH 2 IO + O 2 CH 2 O 2 + CH 2 O 2 → 2CH 2 O + O 2

14. Dr. Terry A. Miller Dr. Neal D. Kline Dr. Dmitry Melnik Dr. Mourad Roudjane Henry Tran Dr. Richard Dawes Phalgun Lolur

15. Kinetics If we follow Y. P. Lee’s mechanism, and our upper estimates of the initial concentration of CH 2 I and iodine atoms at 1.0E+15, then the expected half-life time for Criegee is ~ 11 microseconds and for CH 2 IO 2 is about 24 microseconds. The measured value is about 5 microseconds, which makes it look more like Criegee rather than peroxy. W.-L. Ting, C.-H. Chang, Y.-F. Lee, H. Matsui, Y.-P. Lee*, and Jim J.-M. Lin*, J. Chem. Phys. 141, 104308 (2014). R. Atkinson, el al., Atmos. Chem. Phys. 7, 981 (2007) T. Gravestock, M. Blitz, W. Bloss, and D. E. Heard, ChemPhysChem 11, 3928 (2010)

16. Kinetics 0.5 Torr of SO2 would “kill” Criegee almost immediately Even if peroxy does not directly react with SO2, its temporal profile shows faster decay with the addition of SO2. When Criegee depletes faster, the peroxy replenishment channel quenches.