1. 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

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

3. Previous Studies 3 Gas Phase Absorption (440-530 nm) [Porter & Ward] 2 B 1 - 2 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]

4. 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

5. 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

6. PGopher Simulation CRD Spectrum of C 2 6 Band Origin 516.037 nm Rotational Constant(s) B”= 1.624 cm -1 B’ = 1.746 cm -1 Linewidth 0.05 cm -1 Rotational Temperature 100 K Vibrational Temperature

7. Long range scan 7 [Huang]

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

9. 1 2 B 1 - 2 A 1 origin band Origin: 18901.29(3) A: 0.198(1) B: 0.185(1) C: 0.0957(5) Temp (K): 26.6 B3LYP/aug-cc-pVDZ [Tonokura] A’: 0.1964 B’: 0.1846 C’: 0.0952 9 A”: 0.209472(10) B”: 0.186793(7) MW spec [McMahon] C”: 0.098714988(20) Gaussian linewidth: 0.05 cm -1

10. 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) 18901.29(3)00.198(1)0.185(1)0.0957(5)> 0.3 19472.45(3)571.16(6)0.197(1)0.185(1)0.0959(5)> 0.3 19797.41(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'=0.0952 cm -1

11. 2 B 1 - 2 A 1 ( ) Q branch Lorentzian: 0.055 cm -1 Gaussian: 0.05 cm -1 Lifetime = 100 ± 30 ps 11

12. TransitionBand origin (cm -1 ) G( ' ) (cm -1 ) A'(cm -1 )B'(cm -1 )C'(cm -1 ) Excited state lifetime(ns) 18901.29(3)00.198(1)0.185(1)0.0957(5)> 0.3 19472.45(3)571.16(6)0.197(1)0.185(1)0.0959(5)> 0.3 19797.41(3)896.12(6)0.197(1)0.185(1)0.0957(5)0.10(3) Molecular Constants for the Phenyl Radical 12 1-  errors are given in parenthesis. Equilibrium rotational constants from TDDFT calculations [Tonokura]: A'=0.1964, B'=0.1864, C'=0.0952 cm -1

13. 13 Oscillator Strength [Kim] = 0.0016   rad = 2.8  s (CASSCF(7,13)/6-311+G**) Fluorescence quantum yield ~ 3.4x10 -5 1 2 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]

14. The Optimized Geometry X2A1X2A1 12B112B1 A: 0.209472(10) B: 0.186793(7) C: 0.098714988(20) 1.0841 1.380 1.399 1.407 125.9 116.5 120.2 120.6 Tonokura B3LYP/aug-cc-pVDZ A: 0.2085 B: 0.1860 C: 0.0983 1.471 1.419 112.2 124.4 1.379 Tonokura B3LYP/aug-cc-pVDZ A: 0.1964 B: 0.1846 C: 0.0952 MW Spec [McMahon] 124.5 117.2 14 A: 0.197 B: 0.185 C: 0.0957 Our Values

15. 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

16. 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

17. 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) 4364. J. Pacansky, J. Bargon, J. Am. Chem. Soc. 97 (1975) 6896. J.H. Miller, L. Andrews, P.A. Lund, P.N. Schatz, J. Chem. Phys. 73 (1980) 4932. 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) 9733. 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) 1977. J. Park, S. Burova, A.S. Rodgers, M.C. Lin, Chem. Phys. Process Combust. (1999) 308.

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20. Extra Geometry From: 2 B 1 (v’=9) 1.0843 1.0851 1.0841 1.4046 1.4260 126.0 116.5 120.2 120.6 1.4336 Ring Growth A: 0.2016 B: 0.1801 C: 0.0951 A: 0.1976 B: 0.1852 C: 0.0951 Factor Dev = dA+dB+dC Dev 20

21. Random test using ground state Gaussview Structure to B3LYP structure A: 0.209472(10) B: 0.186793(7) C: 0.098714988(20) 1.0843 1.0851 1.0841 1.3745 1.3954 1.4029 126.0 116.5 120.2 120.6 A: 0.2099 B: 0.1874 C: 0.0990 B3LYP MW Spec  ~ 0.0005 0.283 Å maximum deviation Changing only three C atoms 10 6 changes = 100 positions per atom=0.00566 Å step size A 0.01 Å change in a C changes roto by 0.0006 max All C-C bonds ~ 1.4 Å 1)Change Geometry 2)Calculate A,B,C 3)Compare with Actual (B3LYP) ~120 21

22. ~ 179 +/- 11 out of one million C1C2C3 A1 A2 A3A4 1.0843 1.0851 1.0841 1.3745 1.3954 126.0 116.5 120.2 120.6 C1 C2 1.4029 C3 A1 A2 A3 A4 C1 = 1.3860 +/- 0.0040 C2 = 1.4306 +/- 0.0035 C3 = 1.3821 +/- 0.0041 A1 = 120.169 +/- 0.822 A2 = 120.004 +/- 0.871 A3 = 120.023 +/- 0.665 A4 = 119.777 +/- 0.392 From 5 trials…. 22

23. 1.0843 1.0851 1.0841 1.3745 1.3954 126.0 116.5 120.2 120.6 C1 C2 1.4029 C3 A1 A2 A3 A4 C1 = 1.3860 +/- 0.0040 C2 = 1.4306 +/- 0.0035 C3 = 1.3821 +/- 0.0041 A1 = 120.169 +/- 0.822 A2 = 120.004 +/- 0.871 A3 = 120.023 +/- 0.665 A4 = 119.777 +/- 0.392 From 5 trials…. 2 B 1 (v’=0) 1.471 1.419 112.2 124.4 1.379 124.5 117.2 2 A 1 (v”=0) C1 = 1.3953 +/- 0.0036 C2 = 1.4928 +/- 0.0035 C3 = 1.3782 +/- 0.0019 A1 = 120.563 +/- 0.193 A2 = 119.637 +/- 0.181 A3 = 118.564 +/- 0.259 A4 = 122.635 +/- 0.290 From 5 trials…. ~ 179 +/- 11 out of one million~ 326 +/- 7 out of one million 23