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 ~~ ~ ~

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

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

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).

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, %. 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

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, (2007).

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

Benzyl Radical

Rot. Temp ≈ 20K

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

Phenoxy Radical Ar C2C2 ν

Optimized Geometry C2 C1 C3 C4 C5 C6 LevelB3LYP TDDFT Basiscc-pVDZ StateXAB X-AX-B rCO rC1C rC2C rC3C rC2H rC3H rC4H aC6C1C aC1C2C aC2C3C aC1C2H aC4C3H Values of r = Å Values of a = degrees H1 H2 H3 H4 H5

(Values in cm -1 )B3LYP TDDFT Basiscc-pVDZ E. stateXx0.967B X-B A A A A A A A A A A A A A A B B B B B B B B B B B B B B B B

Theoretical Results Ground State A: B: C: Excited State A: B: C:

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

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

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

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!

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, (2007).