Structure in the Visible Absorption Bands of Jet-Cooled Phenyl Peroxy Radicals Michael N. Sullivan *, Keith Freel, J. Park, M.C. Lin, and Michael C. Heaven

Overview Motivation Previous studies Experimental setup – Cavity ringdown – Supersonic jet expansion Phenyl peroxy radical – Experimental results – Theoretical results Summary

Phenyl Peroxy Phenyl Peroxy (C 6 H 5 O 2 ) – Combustion (PAH formation) – Atmospheric Formed through reaction with O 2 Stable, or rearranges to 2- oxepinoxy, cyclopentadienyl Tokmakov, I. V.; Kim, G.-S.; Kislov, V. V.; Mebel, A. M.; Lin, M.C. J. Phys. Chem. A 2005, 109, 6114−27.

Previous Studies Phenyl Peroxy – Few spectroscopic studies IR spectra in matrix Low res. visible absorption spectrum – transition first observed by Lin et al. – transition reported by Miller et al. Coupled with electronic structure calculations B 2 A’’ ← X 2 A’’ ~~ A 2 A’ ← X 2 A’’ ~~ Yu, T.; Lin, M.C. J. Am. Chem. Soc. 1994, 116,

Cavity Ringdown Spectroscopy τ = L /c(1-R) PMT RR R R Absorbing Sample Added Empty Cavity R at 540 nm, %, (τ = 66 μs) I(t) = I 0 exp{-[(1-R) + αL](tc/L)} α = absorption coefficient t = time τ = ringdown time L = length of cavity R = mirror reflectivity I = intensity τ = L /c(1-R + αL) α = 1/c ((1/τ 1 ) –(1/τ 2 ))

Excimer Pumped Dye Laser Mirror Curtains Valves/Discharge PMT Computer Cavity Mirror Vacuum Chamber Three continuous flow 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 [Maier], [Miller], [Biennier]

Experimental Conditions Bromobenzene (C 6 H 5 Br) precursor – Argon carrier gas – O 2 added via needle valve – No heating 1 kΩ, 800 V, 65 mA Continuous valves Slit width - 1 mm 7 mm detection distance 540 & 500 nm mirrors, R = % (τ = 40 µs)

Phenyl Peroxy Radical C2C2 C2C2 Phenyl * * * *

Theoretical Calculations Utilized Gaussian 09 Optimized geometry / normal mode – UB3LYP – TD-DFT Spectral simulation – Franck-Condon approximation – PGOPHER

Optimized Geometry LevelUB3LYP TDDFT Basiscc-pVDZaug-cc-pVTZcc-pVDZaug-cc-pVTZ StateXXB BX-B r O-O r C-O r C1-C r C6-C r C5-C r C4-C r C3-C r C2-C r C6-H r C5-H r C4-H r C3-H r C2-H a O2-O1-C a O1-C1-C a C2-C1-C a C1-C6-C a C6-C5-C a C5-C4-C a C4-C3-C a C3-C2-C a C1-C6-H a C4-C5-H a C1-C2-H a C4-C3-H

Theoretical Results A'' A" x(b) y (a) z (c) SOMO A' A"

0-0 Band aug-cc-pVDZaug-cc-pVTZ

0-0 Band aug-cc-pVDZaug-cc-pVTZ

0-0 Band aug-cc-pVDZaug-cc-pVTZ Origin: 17,519 cm -1 Lorenztian: 2.2 cm -1 T: 34K

0-0 Band aug-cc-pVDZaug-cc-pVTZ Origin: 17,519 cm -1 Lorenztian: 2.2 cm -1 (2.1 ps lifetime) T: 34K

Contributing Normal Modes Mode:  Assignment:         G(v’) (cm -1 )  TDDFT          

Stick spectrum shift: 296 cm -1

Summary Detection of discharge generated phenyl peroxy radicals by CRDS in a jet expansion Determined excited state lifetimes to be 2.1 ps Vibronic spectrum simulated using TDDFT calculations matches well with experimental data Accounts for lack of structure at room temperature. Examine higher energy bands Future work on this project will focus on other PAH species and photolysis

Acknowledgements Group Members and Colleagues: Dr. Jiande Han, Kyle Mascaritolo, Joshua Bartlett Cody Anderson at the Emory Machine Shop Dr. Michael McCarthy for loan of 540 nm mirrors Thank you for listening!

References G. Porter and F.J. Wright, Trans. Faraday Soc. 51, 1469 (1955). J.G. Radziszewski, M. Gil, A.Gorski, J. Spanget-Larsen, J. Waluk, and B.J. Mroz, J. Chem. Phys. 115, 9733 (2001). K. Tonokura, T. Ogura, and M. Koshi, J. Phys. Chem. A 108, 7801 (2004.) Tokmakov, I. V.; Kim, G.-S.; Kislov, V. V.; Mebel, A. M.; Lin, M.C. J. Phys. Chem. A 2005, 109, 6114−27 A. Mardyukov and W. Sander, Chemistry - A European Journal 15, 1642 (2009.) S. Naumov and C. Von Sonntag, J. Phys. Org. Chem. 18, 586 (2005.) T. Yu and M.C. Lin, J. Am. Chem. Soc. 116, 9571 (1994.) G.M. Just, E.N. Sharp, S.J. Zalyubovsky, and T.A. Miller, Chem. Phys. Lett. 417, 378 (2006.) 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.)

Theory and Experiment

aug-cc-pVTZ LevelB3LYPTDDFT Basis Setaug-cc-pVTZ Electronic State X̃ 2 A"Ã 2 A'B̃ 2 A"C̃ 2 A" r OO r CO r C 1 C r C 6 C r C 5 C r C 4 C r C 3 C r C 2 C r C 6 H r C 5 H r C 4 H r C 3 H r C 2 H a O 8 O 7 C a O 7 C 1 C a C 2 C 1 C a C 1 C 6 C a C 6 C 5 C a C 5 C 4 C a C 4 C 3 C a C 3 C 2 C a C 1 C 6 H a C 4 C 5 H a C 1 C 2 H a C 4 C 3 H a C 5 C 4 H aug-cc-pVDZ LevelB3LYPTDDFT Basis Setaug-cc-pVDZ Electronic StateX̃ 2 A"Ã 2 A'B̃ 2 A"C̃ 2 A" r OO r CO r C 1 C r C 6 C r C 5 C r C 4 C r C 3 C r C 2 C r C 6 H r C 5 H r C 4 H r C 3 H r C 2 H a O 8 O 7 C a O 7 C 1 C a C 2 C 1 C a C 1 C 6 C a C 6 C 5 C a C 5 C 4 C a C 4 C 3 C a C 3 C 2 C a C 1 C 6 H a C 4 C 5 H a C 1 C 2 H a C 4 C 3 H a C 5 C 4 H