Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Spectroscopic identification of isomeric trimethylbenzyl radicals generated in corona discharge of tetramethylbenzene Young Wook Yoon, Gi Woo Lee, Sang Kuk Lee Department of Chemistry and The Chemistry Institute for Functional Materials Pusan National University Pusan , South Korea The 66 th International Symposium on Molecular Spectroscopy, RJ05 Columbus, Ohio, June 20-24, 2011

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Motivation (CH 3 ) 2 CH 3 (CH 3 ) 3 (CH 3 ) 2 (done) JOURNAL OF MOLECULAR SPECTROSCOPY 137, (1989) JOURNAL OF MOLECULAR SPECTROSCOPY 194, (1999) J. Phys. Chem. A 2003, 107,

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Durene 2,4,5-trimethylbenzyl Motivation (done) THE JOURNAL OF CHEMICAL PHYSICS 126, isomers 3 isomers This work

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Contents 1. Introduction - Benzyl type radicals 2. Experimental - CESE system 3. Results & discussion - 1,2,3,4-tetramethylbenzene - 1,2,3,5-tetramethylbenzene 4. Conclusion

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea 1.Planar structure with 7 delocalized  electrons 2.Many vibrational modes with similar frequencies 2 nd Excited state : (1b 2 ) 2 (2b 2 ) 1 (1a 2 ) 2 (3b 2 ) B 2 1 st Excited state : (1b 2 ) 2 (2b 2 ) 2 (1a 2 ) 1 (3b 2 ) A 2 Ground state : (1b 2 ) 2 (2b 2 ) 2 (1a 2 ) 2 (3b 2 ) B 2 Benzyl-type radicals H H X Proto-type Aromatic Molecular Radicals

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea φ1φ1 φ2φ2 φ3φ3 φ4φ4 φ5φ5 φ6φ6 φ7φ7 b2b2 b2b2 a2a2 b2b2 a2a2 b2b2 b2b2 benzyl-type radical Molecular orbitals of benzyl-type radical

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea D1D1 D0D0 D2D2 2B22B2 2B22B2 2A22A2 B-type (visible region) A-type Theoretically, D 2 → D 0, D 1 → D 0 are allowed. 800cm 22000cm Energy levels of benzyl radical Collisional relaxation via vibronic coupling Experimentally, only D 1 → D 0 is observed.

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Experimental : CESE system

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Overview of CESE system

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Discharge in CESE Jet emission in CESE system Demonstration with He gas

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea CESE Spectra Carrier gas(He) + Sample Vacuum Chamber Supersonic Jet Expansion Advantage of CESE system - Excellent S/N ratio - Decreasing Doppler broadening - Simplification of spectrum - Powerful technique for transient species P o = 3 atm (Glass) P v = 1 Torr Voltage = ~1.5 kV Current = 5mA P0P0 Emission PvPv CESE system Corona Excited Supersonic Expansion (+) (-) e-e- Corona Discharge

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea CESE vs. LIF-DF (p-fluorobenzyl) LIF- DF spectrum J. Chem. Phys. 1990, 93, 8488 * He atomic line * * * CESE spectrum Chem. Phys. Lett. 1999,

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Mechanism of vibronic emission X * X X e-e- S0S0 SnSn − ·H− ·H D0D0 Collisional relaxation D1D1 CESE Spectrum Origin band Emission * X Radical formation CESE Spectrum gives vibrational information on radicals in the ground state

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Radicals from 1,2,3,4-tetramethylbenzene 2,3,6-trimethylbenzyl radical 2,3,4-trimethylbenzyl radical 1,2,3,4-tetramethylbenzene

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Spectrum from 1,2,3,4-tetramethylbenzene 2,3,6- 2,3,4-

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea

Solid Gas

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Radicals from 1,2,3,5-tetramethylbenzene 1,2,3,5- tetramethylbenzene 2,4,6- trimethylbenzyl radical 3,4,5- trimethylbenzyl radical 2,3,5- trimethylbenzyl radical

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Spectrum from 1,2,3,5-tetramethylbenzene 2,4,6- 3,4,5- 2,3,5- * * * * *

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea

SolidGas

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Origin bands in the D 1 → D 0 transition of methyl-substituted benzyl radicals This work

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Origin bands in the D 1 → D 0 transition of methyl-substituted benzyl radicals From 1,2,3,4-tetramethylbenzene

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Origin bands in the D 1 → D 0 transition of methyl-substituted benzyl radicals From 1,2,3,5-tetramethylbenzene

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Conclusion 1.Applied CESE system for vibronic emission spectroscopy of benzyl-type radicals. 2.Observed many substituted benzyl-type radicals in the gas phase. 3.Detected new spectroscopic evidence of trimethylbenzyl radicals(2,3,4-, 2,3,6-, 2,3,5-, 3,4,5-, 2,4,6-). 4.Proper selection of a precursor plays a key role in observation of transient species.

Laboratory of Molecular Spectroscopy, Pusan National University, Pusan, Republic of Korea Thank you for your attention