Cavity ring down spectroscopy on C 6 H 5 radical in a pulsed supersonic jet expansion discharge Keith Freel Dr. Michael Heaven Dr. M.C. Lin Dr. Joonbum Park 1

Phenyl C 6 H 5 Combustion (PAH Formation) Astrophysics Environmental Impact Computational Benchmark Small Absorption Coefficient (in vis region) 2

Previous Studies 3 Gas Phase Absorption ( nm) [Porter & Ward] 2 B A 1 n   Electron Spin Resonance [Bennett, Kasai] C 2V symmetry Unpaired electron in non-bonding  -orbital Matrix Isolation Studies [Friderichesen], [Radziszewski], [Pacansky], [Miller], [Engert], [Park] IR and UV Spectroscopy [Tonokura] Recent Gas Phase Studies Electronic Spectroscopy by CRDS [Lin],[Tonokura] Microwave Spectroscopy [McMahon] High Resolution IR Spectroscopy [Sharp]

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 [Maier], [Miller], [Biennier] 4

Cavity Ring-Down Spectroscopy Loss = (2  l )(tc/2L) Total loss = [(1-R)+  l ] (tc/L) PMT RR l e -1 x 100 = 36.8   w/ abs  12  s   empty  18  s PMT R R Absorbing Sample Added Empty Cavity ~ 5000 passes at 18  s (path length from 0.10 m to 500 m) 5  = 1.16x10 -5 cm -1

PGopher Simulation CRD Spectrum of C 2 6 Band Origin nm Rotational Constant(s) B”= cm -1 B’ = cm -1 Linewidth 0.05 cm -1 Rotational Temperature 100 K Vibrational Temperature

Long range scan 7 [Huang]

Simulation of C 2 Swan Band T rot = 30 K T vib ~ 5,000 K 8 [PGOPHER] Gaussian linewidth: 0.05 cm -1

1 2 B A 1 origin band Origin: (3) A: 0.198(1) B: 0.185(1) C: (5) Temp (K): 26.6 B3LYP/aug-cc-pVDZ [Tonokura] A’: B’: C’: A”: (10) B”: (7) MW spec [McMahon] C”: (20) Gaussian linewidth: 0.05 cm -1

Molecular Constants for the Phenyl Radical 10 TransitionBand origin (cm -1 ) G( ' ) (cm -1 ) A'(cm -1 )B'(cm -1 )C'(cm -1 ) Excited state lifetime(ns) (3)00.198(1)0.185(1)0.0957(5)> (3)571.16(6)0.197(1)0.185(1)0.0959(5)> (3)896.12(6)0.197(1)0.185(1)0.0957(5)0.10(3) 1-  errors are given in parenthesis. Equilibrium rotational constants from TDDFT calculations [Tonokura]: A'=0.1964, B'=0.1864, C'= cm -1

2 B A 1 ( ) Q branch Lorentzian: cm -1 Gaussian: 0.05 cm -1 Lifetime = 100 ± 30 ps 11

TransitionBand origin (cm -1 ) G( ' ) (cm -1 ) A'(cm -1 )B'(cm -1 )C'(cm -1 ) Excited state lifetime(ns) (3)00.198(1)0.185(1)0.0957(5)> (3)571.16(6)0.197(1)0.185(1)0.0959(5)> (3)896.12(6)0.197(1)0.185(1)0.0957(5)0.10(3) Molecular Constants for the Phenyl Radical  errors are given in parenthesis. Equilibrium rotational constants from TDDFT calculations [Tonokura]: A'=0.1964, B'=0.1864, C'= cm -1

13 Oscillator Strength [Kim] =   rad = 2.8  s (CASSCF(7,13)/6-311+G**) Fluorescence quantum yield ~ 3.4x B 1  X 2 A 1 - Energy Transfer For 1 2 B 1 ( 9 = 1) the lifetime was 100 ns 21,000 cm -1 26,600 cm -1 [Lin], [Negru]

The Optimized Geometry X2A1X2A1 12B112B1 A: (10) B: (7) C: (20) Tonokura B3LYP/aug-cc-pVDZ A: B: C: Tonokura B3LYP/aug-cc-pVDZ A: B: C: MW Spec [McMahon] A: B: C: Our Values

Conclusions Detection of discharge generated phenyl radical by CRDS in a jet expansion. Measured G( ' ) and rotational constants for three fundamental modes. Excited state lifetime is about 100 ps at 9 =1. Rotational constants match best with constants from DFT calculation by Tonokura et al. 15

Thanks to: Group Members and Colleagues: Dr Jeremy Merritt, Dr Humayun Kabir, Dr Beau Barker, Ivan Antonov, Dr Jiande Han, Kyle Mascaritolo, Luis Mendoza, Dr Shucheng Xu Cody Anderson at the Emory Machine Shop Thank you for listening! 16

References 17 Porter G.; Ward B. Proc. R. Soc. London, Ser. A 1965, 287, 457. J.E. Bennett, B. Mile, A. Thomas, Chem. Comm. London (1965) 265. J.E. Bennett, B. Mile, A. Thomas, Proc. Royal Soc. London, Series A: Mathemat. Phys. Eng. Sci. 293 (1966) 246. P.H. Kasai, E. Hedaya, E.B. Whipple, J. Am. Chem. Soc. 91 (1969) J. Pacansky, J. Bargon, J. Am. Chem. Soc. 97 (1975) J.H. Miller, L. Andrews, P.A. Lund, P.N. Schatz, J. Chem. Phys. 73 (1980) J.G. Radziszewski, Chem. Phys. Lett. 301 (1999) 565. J.G. Radziszewski, M. Gil, A. Gorski, J. Spanget-Larsen, J. Waluk, B.J. Mroz, J. Chem. Phys. 115 (2001) J.M. Engert, B. Dick, Appl. Phys. B Lasers Opt. 63 (1996) 531. A.V. Friderichsen, J.G. Radziszewski, M.R. Nimlos, P.R. Winter, D.C. Dayton, D.E. David, G.B. Ellison, J. Am. Chem. Soc. 123 (2001) J. Park, S. Burova, A.S. Rodgers, M.C. Lin, Chem. Phys. Process Combust. (1999) 308.

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Extra Geometry From: 2 B 1 (v’=9) Ring Growth A: B: C: A: B: C: Factor Dev = dA+dB+dC Dev 20

Random test using ground state Gaussview Structure to B3LYP structure A: (10) B: (7) C: (20) A: B: C: B3LYP MW Spec  ~ Å maximum deviation Changing only three C atoms 10 6 changes = 100 positions per atom= Å step size A 0.01 Å change in a C changes roto by max All C-C bonds ~ 1.4 Å 1)Change Geometry 2)Calculate A,B,C 3)Compare with Actual (B3LYP) ~120 21

~ 179 +/- 11 out of one million C1C2C3 A1 A2 A3A C1 C C3 A1 A2 A3 A4 C1 = / C2 = / C3 = / A1 = / A2 = / A3 = / A4 = / From 5 trials…. 22

C1 C C3 A1 A2 A3 A4 C1 = / C2 = / C3 = / A1 = / A2 = / A3 = / A4 = / From 5 trials…. 2 B 1 (v’=0) A 1 (v”=0) C1 = / C2 = / C3 = / A1 = / A2 = / A3 = / A4 = / From 5 trials…. ~ 179 +/- 11 out of one million~ 326 +/- 7 out of one million 23