1. Cavity Ringdown Spectroscopy of the A 2 A 2 - B 2 B 2 Vibronically Mixed Excited States of the Benzyl Radical and the 1 2 A 2 ← X 2 B 1 Transition of the Phenoxy Radical in a Supersonic Expansion Michael N. Sullivan *, Keith Freel, J. Park, M.C. Lin, and Michael C. Heaven ~~ ~ ~

2. Soot Formation and PAH’s D’Anna, A.; Violi, A.; D’Alessio, A. Combust. Flame 121, 418 (2000).

3. Benzyl and Phenoxy Radicals Benzyl (C 6 H 5 CH 2 ) – Combustion (PAH formation) Phenoxy (C 6 H 5 O) – Combustion (PAH formation) – Atmospheric & biological

4. Previous Studies Phenoxy – First obs. by Porter and Wright 1 – Numerous studies (see ref. 2 ) – Conflicting results – Recent work Matrix isolation studies in the UV and Vis regions by Radziszewski et al. 2 Cavity ringdown studies in the UV by Tonokura et al. 3 Theoretical study of the first excited state by Witek et al. 4 Benzyl – First obs. by Schüler et al. 5 – LIF studies in a supersonic jet by Miller et al. 6,7 – A 2 A 2 - B 2 B 2 vibronically mixed excited states studied previously by Widen and Weisshaar 8 ~~ 1 Porter, G. and Wright, F.J., Trans. Faraday Soc. 51, 1469 (1955). 2 Radziszewski, J. G.; Gil, M.; Gorski, A.; Spanget-Larsen, J.; Waluk, J.; Mroz, B. J., J. Chem. Phys. 115, 9733 (2001). 3 Tonokura, K.; Ogura, T.; Koshi, M., J. Phys. Chem. A 108, 7801 (2004). 4 Cheng, C.; Lee, Y.; Witek, H., J. Phys. Chem. A 112, 2648 (2008). 5 Schüler, H.; Reinebeck, L.; Kaberle, A.R., Z. Naturforsch. 79, 421 (1952). 6 Heaven, M; DiMauro, L.; Miller, T.A., Chem. Phys. Lett. 95, 347 (1983). 7 Lin, T.; Tan, X.; Cerny, T.; Williamson, J.; Cullin, D.; Miller, T.A., Chem. Phys. 167, 203 (1992). 8 Eiden, G. and Weisshaar, J., J. Chem. Phys. 104, 8896 (1996).

5. Cavity Ring-Down Spectroscopy Loss = (2αL)(tc/2L) Total loss = [(1-R)+ αL] (tc/L) PMT RR R R Absorbing Sample Added Empty Cavity R at 620 nm, 99.9985%. Pathlength of 6 km. I(t) = I 0 exp{-[(1-R) + αL](tc/L)] α = absorption coefficient t = time L = length of cavity R = mirror reflectivity I = intensity

6. Excimer Pumped Dye Laser Mirror Curtains Valves/Discharge PMT Computer Cavity Mirror Vacuum Chamber Three Pulsed Solenoid Valves 1 1. Ground Plate 2. Phenolic Insulator 3. High Voltage Jaw 2 3 Experimental Setup Radical Production – Electrical Discharge – Jet Expansion Cooling Radical Detection – Cavity Ringdown Spectroscopy H. Linnartz, O. Vaizert, P. Cias, L. Gruter, and J. Maier, Chem. Phys. Lett. 345, 89 (2001). L. Biennier, F. Salama, L. J. Allamandola, and J. J. Scherer, J. Chem. Phys. 118, 7863 (2003). W. Shenghai, P. Dupre, P. Rupper, and T. A. Miller, J. Chem. Phys. 127, 224305 (2007).

7. Experimental Conditions Precursor – benzyl chloride (C 6 H 5 CH 2 Cl) 1% precursor in 1 atm back pressure Ar (at 60 °C) 3 pinhole pulsed expansion – 900V – 100 mA – Slit width: 0.5 mm – Detection distance: 8 mm

8. Benzyl Radical

9. Rot. Temp ≈ 20K

10. Experimental Conditions Precursor – anisole (C 6 H 5 OCH 3 ) 1% precursor in.6 atm back pressure Ar (at 24°C) 3 pinhole pulsed expansion – 1200V – 100 mA – Slit width: 0.8 mm – Detection distance: 8 mm

11. Phenoxy Radical Ar C2C2 ν 11 1 0 2 0 3 0

12. Optimized Geometry C2 C1 C3 C4 C5 C6 LevelB3LYP TDDFT Basiscc-pVDZ StateXAB X-AX-B rCO1.2561.3231.244 -0.0670.012 rC1C21.4551.4131.451 0.0410.004 rC2C31.3801.3941.439 -0.014-0.059 rC3C41.4121.3971.394 0.0150.018 rC2H11.0921.0901.093 0.002-0.001 rC3H21.093 1.094 0.000-0.002 rC4H31.0921.0911.089 0.0010.004 aC6C1C2117.0119.9111.7 -2.9175.312 aC1C2C3121.0119.2123.6 1.733-2.602 aC2C3C4120.2121.4122.4 -1.165-2.158 aC1C2H1116.9119.1117.3 -2.263-0.460 aC4C3H2119.5120.2119.7 -0.702-0.233 Values of r = Å Values of a = degrees H1 H2 H3 H4 H5

13. (Values in cm -1 )B3LYP TDDFT Basiscc-pVDZ E. stateXx0.967B X-B A1528.31511515498 -13 A1809.11782814787 5 A1978.37946968936 -10 A11011.6297810401005 27 A11151.92111411661127 13 A11413.92136714131367 A11485.36143615811529 93 A11594.58154216301576 34 A13174.85307031723067 -3 A13196.61309131943089 -3 A13207.80310232303123 21 A2381.19369335324 -44 A2810.79784836809 25 A2990.27958979947 -11 B1194.71188109106 -83 B1488.67473413400 -73 B1660.97639530512 -127 B1807.17781765739 -41 B1933.46903863834 -68 B11007.24974984952 -22 B2443.38429430416 -13 B2595.50576593574 -2 B21082.6310471019985 -61 B21155.69111811651126 9 B21272.08123012451204 -27 B21344.49130013561312 12 B21443.05139514291382 -14 B21549.28149816201567 69 B23181.75307731753070 -6 B23204.41309931933088 -11

14. Theoretical Results Ground State A: 0.1832835 B: 0.0923975 C: 0.0614295 Excited State A: 0.1938119 B: 0.0865032 C: 0.0598089

15. Rot. Temp ≈ 45K Rot. Temp ≈ 20K Excited state lifetime ≈ 88 +/- 10 fs Lorenztian ≈ 60 cm -1 FWHM

16. Rot. Temp ≈ 45K Rot. Temp ≈ 20K Excited state lifetime ≈ 88 +/- 10 fs Lorenztian ≈ 60 cm -1 FWHM

17. Summary Detection of discharge generated benzyl and phenoxy radicals by CRDS in a jet expansion Determined excited state lifetime for the phenoxy radical to be 88 +/- 10 fs Vibronic spectrum simulated using TDDFT calculations match well with experimental data Future work on this project will focus on the phenyl peroxy (C 6 H 5 O 2 ) radical and is currently in progress

18. Acknowledgements Group Members and Colleagues: Dr. Jiande Han, Ivan Antonov, Kyle Mascaritolo, Joshua Barlett, Chien-Lin Tseng Cody Anderson at the Emory Machine Shop Dept. of Energy Thank you for listening!

19. References D’Anna, A.; Violi, A.; D’Alessio, A. Combust. Flame 121, 418 (2000). Porter, G. and Wright, F.J., Trans. Faraday Soc. 51, 1469 (1955). Radziszewski, J. G.; Gil, M.; Gorski, A.; Spanget-Larsen, J.; Waluk, J.; Mroz, B. J., J. Chem. Phys. 115, 9733 (2001). Tonokura, K.; Ogura, T.; Koshi, M., J. Phys. Chem. A 108, 7801 (2004). Cheng, C.; Lee, Y.; Witek, H., J. Phys. Chem. A 112, 2648 (2008). Schüler, H.; Reinebeck, L.; Kaberle, A.R., Z. Naturforsch. 79, 421 (1952). Heaven, M; DiMauro, L.; Miller, T.A., Chem. Phys. Lett. 95, 347 (1983). Lin, T.; Tan, X.; Cerny, T.; Williamson, J.; Cullin, D.; Miller, T.A., Chem. Phys. 167, 203 (1992). Eiden, G. and Weisshaar, J., J. Chem. Phys. 104, 8896 (1996). H. Linnartz, O. Vaizert, P. Cias, L. Gruter, and J. Maier, Chem. Phys. Lett. 345, 89 (2001). L. Biennier, F. Salama, L. J. Allamandola, and J. J. Scherer, J. Chem. Phys. 118, 7863 (2003). W. Shenghai, P. Dupre, P. Rupper, and T. A. Miller, J. Chem. Phys. 127, 224305 (2007).