Post on 05-Jan-2016
Cavity Ringdown Spectroscopy of the A 2A2 - B 2B2 Vibronically Mixed Excited
States of the Benzyl Radical and the 1 2A2 ← X 2B1 Transition of the Phenoxy
Radical in a Supersonic Expansion
Michael N. Sullivan*, Keith Freel, J. Park, M.C. Lin, and Michael C. Heaven
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Soot Formation and PAH’s
D’Anna, A.; Violi, A.; D’Alessio, A. Combust. Flame 121, 418 (2000).
Benzyl and Phenoxy Radicals
• Benzyl (C6H5CH2)– Combustion (PAH formation)
• Phenoxy (C6H5O)– Combustion (PAH formation)– Atmospheric & biological
Previous Studies
• Phenoxy– First obs. by Porter and Wright1
– 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 2A2 - B 2B2 vibronically mixed excited states studied previously by Widen and Weisshaar8
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1Porter, G. and Wright, F.J., Trans. Faraday Soc. 51, 1469 (1955).2Radziszewski, J. G.; Gil, M.; Gorski, A.; Spanget-Larsen, J.; Waluk, J.; Mroz, B. J., J. Chem. Phys. 115, 9733 (2001).3Tonokura, K.; Ogura, T.; Koshi, M., J. Phys. Chem. A 108, 7801 (2004).4Cheng, C.; Lee, Y.; Witek, H., J. Phys. Chem. A 112, 2648 (2008).5Schüler, H.; Reinebeck, L.; Kaberle, A.R., Z. Naturforsch. 79, 421 (1952).6Heaven, M; DiMauro, L.; Miller, T.A., Chem. Phys. Lett. 95, 347 (1983).7Lin, T.; Tan, X.; Cerny, T.; Williamson, J.; Cullin, D.; Miller, T.A., Chem. Phys. 167, 203 (1992).8Eiden, G. and Weisshaar, J., J. Chem. Phys. 104, 8896 (1996).
Cavity Ring-Down SpectroscopyLoss = (2αL)(tc/2L) Total loss = [(1-R)+ αL] (tc/L)
PMTR R
PMTRR
Absorbing Sample Added
Empty Cavity
R at 620 nm, 99.9985%. Pathlength of 6 km.
I(t) = I0 exp{-[(1-R) + αL](tc/L)]
α = absorption coefficient t = timeL = length of cavityR = mirror reflectivityI = intensity
Excimer Pumped Dye Laser
Mirror Curtains
Valves/Discharge
PMT
Computer
Cavity MirrorCavity Mirror
Vacuum Chamber
Three Pulsed Solenoid Valves
1
1. Ground Plate2. Phenolic Insulator3. 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).
Experimental Conditions
• Precursor – benzyl chloride (C6H5CH2Cl)
• 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
445.7 445.8 445.9 446.03.00E-009
4.00E-009
5.00E-009
6.00E-009
7.00E-009
Wavelength (nm)
446.6 446.7 446.8 446.9
3.00E-009
6.00E-009
9.00E-009
1.20E-008
Wavelength (nm)
447.8 447.9 448.0 448.1
6.00E-009
1.20E-008
1.80E-008
2.40E-008
Wavelength (nm)
Benzyl RadicalRot. Temp ≈ 20K
Experimental Conditions
• Precursor – anisole (C6H5OCH3)
• 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
C2
ν11 1
0
ν11 20
ν11 30
Optimized Geometry
C2C1
C3
C4C5
C6
Level B3LYP B3LYP TDDFT
Basis cc-pVDZ cc-pVDZ cc-pVDZ
State X A B X-A X-B
rCO 1.256 1.323 1.244 -0.067 0.012
rC1C2 1.455 1.413 1.451 0.041 0.004
rC2C3 1.380 1.394 1.439 -0.014 -0.059
rC3C4 1.412 1.397 1.394 0.015 0.018
rC2H1 1.092 1.090 1.093 0.002 -0.001
rC3H2 1.093 1.093 1.094 0.000 -0.002
rC4H3 1.092 1.091 1.089 0.001 0.004
aC6C1C2 117.0 119.9 111.7 -2.917 5.312
aC1C2C3 121.0 119.2 123.6 1.733 -2.602
aC2C3C4 120.2 121.4 122.4 -1.165 -2.158
aC1C2H1 116.9 119.1 117.3 -2.263 -0.460
aC4C3H2 119.5 120.2 119.7 -0.702 -0.233
Values of r = ÅValues of a = degrees
H1
H2
H3
H4
H5
(Values in cm-1 ) B3LYP TDDFT
Basis cc-pVDZ cc-pVDZ
E. state X x0.967 B x0.967 X-BA1 528.31 511 515 498 -13A1 809.11 782 814 787 5A1 978.37 946 968 936 -10A1 1011.62 978 1040 1005 27A1 1151.92 1114 1166 1127 13A1 1413.92 1367 1413 1367 -1A1 1485.36 1436 1581 1529 93A1 1594.58 1542 1630 1576 34A1 3174.85 3070 3172 3067 -3A1 3196.61 3091 3194 3089 -3A1 3207.80 3102 3230 3123 21
A2 381.19 369 335 324 -44A2 810.79 784 836 809 25A2 990.27 958 979 947 -11
B1 194.71 188 109 106 -83B1 488.67 473 413 400 -73B1 660.97 639 530 512 -127B1 807.17 781 765 739 -41B1 933.46 903 863 834 -68B1 1007.24 974 984 952 -22
B2 443.38 429 430 416 -13B2 595.50 576 593 574 -2B2 1082.63 1047 1019 985 -61B2 1155.69 1118 1165 1126 9B2 1272.08 1230 1245 1204 -27B2 1344.49 1300 1356 1312 12B2 1443.05 1395 1429 1382 -14B2 1549.28 1498 1620 1567 69B2 3181.75 3077 3175 3070 -6B2 3204.41 3099 3193 3088 -11
Theoretical Results
Ground StateA: 0.1832835 B: 0.0923975 C: 0.0614295
Excited StateA: 0.1938119 B: 0.0865032 C: 0.0598089
Rot. Temp ≈ 45KRot. Temp ≈ 20K
Excited state lifetime ≈ 88 +/- 10 fs
Lorenztian ≈ 60 cm-1 FWHM
Rot. Temp ≈ 45KRot. 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 (C6H5O2) 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,
224305 (2007).