Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Spectroscopic Identification of New Aromatic Molecular Radicals in Corona Discharge: α-Methylbenzyl Radical Chan Ho Park, Gi Woo Lee, Hyeon Geun Ahn, Sang Kuk Lee Department of Chemistry Pusan National University Pusan , Korea The 63 rd International Symposium on Molecular Spectroscopy, WG11 Columbus, Ohio, June 16-20, 2008

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Previous works Mono-substituted benzyl radicals Multi-substituted benzyl radicals X : F, Cl, CH 3, CN X : F, Cl, CH 3

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea D 1 → D 0 (0) D 2 → D 0 (0) C2C2 J. Phys. Chem. A 2007, 111, Mesityl Radical

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Tri-substitution: Duryl Radical J. Chem. Phys. 2007, 126, b

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Substitution at Side Chain Intermediate

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

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea φ1φ1 φ2φ2 φ3φ3 φ4φ4 φ5φ5 φ6φ6 φ7φ7 b2b2 b2b2 a2a2 b2b2 a2a2 b2b2 b2b2 Benzyl Radical Molecular Orbitals of Benzyl Radical

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, 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

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea CESE Spectra Carrier gas(He) + Sample Vacuum Chamber Supersonic Jet Expansion Advantage of CESE - Excellent S/N ratio - Decreasing Doppler broadening - Simplification of spectrum - Powerful technique for transient species P o = 3 atm P v = 10 Torr HV = ~1.5 kV P0P0 Emission PvPv Principle of CESE system Corona Excited Supersonic Expansion (+) (-) e-e- Corona Discharge

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

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

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Discharge in CESE Jet Emission in CESE system

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, 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 & Nano Materials, Pusan National University, Republic of Korea CESE vs. LIF-DF (p-chlorobenzyl)

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Mechanism of formation X * X * X X e-e- S0S0 SnSn − ·H− ·H D0D0 Collisional relaxation D1D1 CESE Spectrum Origin band Emission

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Substitution at Side Chain Precursor : Toluene 6b 1 6a Origin D o (C-H) = 415 kJ/mol -H TolueneBenzyl radical

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Precursor: Ethylbenzene weak intensity: α-methylbenzyl radical(?) Major product Radical α-Methylbenzyl Radical D o (C-C) = 344 kJ/mol D o (C-H) = 415 kJ/mol strong transition: benzyl radical

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Precursor : Isopropylbenzene Major Product origin of α-methylbenzyl radical Radical α-Methylbenzyl Radical D o (C-C) = 344 kJ/mol D o (C-H) = 415 kJ/mol

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea a) Benzyl radical from toluene b) α-Methylbenzyl radical from ethylbenzene The region of C 2 observed Not observed c) α-Methylbenzyl radical from isopropylbenzene origin 6a 6b 1 Comparison of Spectra

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Assignment of α-Methylbenzyl Radical Precursor : Ethylbenzene Calculation : B3LYP/cc-pvdz

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea p-Chloro-α-Methylbenzyl Radical - CH 3 - H

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Spectrum from p-Chloro-Ethylbenzene

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea p-Chlorobenzyl Radical

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea From precursor p-chlorobenzyl radical

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Assignment of p-Chloro-α-Methylbenzyl positionFrom originmodecalculationReference origin b Reference : p-chloro-fluorobenzene Calculation : B3LYP/cc-pvdz

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea - CH 3 - H p-Fluoro-α-Methylbenzyl Radical

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Spectrum from p-Fluoro-Ethylbenzene

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea

Spectrum from precursor p-fluorobenzyl radical ?

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea α-methylbenzylbadical p-chloro-α-methylbenzyl radical p-fluoro-α-methylbenzyl radical Origin band

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Assignment of p-Fluoro-α-Methylbenzyl positionFrom originmodecalculationReference origin b Reference : 1,4-difluorobenzene Calculation : B3LYP/cc-pvdz

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Summary 1.Developed CESE system for spectroscopy of molecular radicals 2.Observed many substituted benzyl radicals in the gas phase. 3.Detected new spectroscopic evidence of α- methylbenzyl radicals for the first time.

Laboratory of Molecular Spectroscopy & Nano Materials, Pusan National University, Republic of Korea Acknowledgments 1.Basic Research Program, Korea Research Foundation 2. Special Basic Research Program, Korea Science and Engineering Foundation Funding for Basic Sciences

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