Md Asmaul Reza, Jahangir Alam, Amy Mason, Neil Reilly and Jinjun Liu Department of Chemistry, University of Louisville JET-COOLED DISPERSED FLUORESCENCE (DF) SPECTROSCOPY OF BRANCHED CHAIN ALKOXY RADICALS 3-methyl-1-butoxy (iso-pentoxy) 2-methyl-1-propoxy (iso-butoxy) 2-methyl-1-butoxy International Symposium on Molecular Spectroscopy University of Illinois Urbana-Champaign 06/26/15 1

Outline 2  Introduction and motivation  Experimental setup  DF spectra and spectral analysis:  Conclusions  Future work  iso-butoxy  2-methyl-1-butoxy  iso-pentoxy

Introduction and Motivation  Alkoxy radicals (RO·) are key intermediates in the oxidation of hydrocarbons both in combustion and in the atmosphere.  Reactions of alkoxy radicals in the atmosphere: i) decomposition ii) reaction with O 2 iii) isomerization (via internal H transfer).  Identification of conformers of alkoxy radicals. Finlayson-Pitts, B. J.; Pitts, J. N. Chemistry of the Upper and Lower Atmosphere; Academic Press: San Diego, Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, (50), Potential energy profiles (kcal/mol) for the ground state decomposition and isomerization reactions of isobutoxy calculated at the B3LYP/ G(d,p) level of theory. i) iii) ii)

Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, (50), Different Conformers of Branched Chain Alkoxy Radicals iso-butoxy 2-methyl-1-butoxy 4 iso-pentoxy

5 Relative energies (Erel, kcal/mol) of conformers of iso-butoxy, 2-methyl-1 butoxy and iso-pentoxy radicasl in the ground state calculated at the B3LYP/ G(d,p) Level of theory. Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, (50), iso-butoxy 2-metyl-1-butoxy iso-pentoxy

6 Experimental LIF/DF Setup DF LIF LIF: laser-induced fluorescence DF: dispersed fluorescence 6 Nd:YAG Pulsed Dye Laser Computer Photolysis Laser Doubling Crystal Vacuum Chamber RONO/He Δν~0.1 cm -1 Nd:YAG ν x3 ν x2 Excitation Laser PMT Box- Car spectrograph iCCD Δν~30 cm -1 OGC PMT=photomultiplier tube; OGC=optogalvanic cell iCCD=intensified charge coupled device

LIF and DF Spectra of Iso-Butoxy Radical Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, (50), ? ? H 2 CO 7 A (28091 cm -1 ) B (28788 cm -1 ) D (B+248 cm -1 ) C (B+142 cm -1 ) * Photolysis Laser Type (II) Type (I)

Comparison of Experimental DF Spectra and FCF Simulation 8 * Photolysis Laser FCF= Franck-Condon factor Mozhayskiy, V. A.; Krylov, A. I. ezSpectrum.

9 n= DF Spectra: Type (II) C (B+142 cm -1 ) D (B+248 cm -1 ) 9 d c V=non CO stretch mode

10 Mixture of CO stretch & CH 3 torsion n= Mixture of CH 3 scissor & C-C stretch mode C-C-C umbrella mode A (28091 cm -1 ) DF Spectrum: Type (I) * Photolysis Laser

d c “Shift Effect” of DF Spectra 11 Calculated

12 Energy ʋ CO +ʋ* ʋ=0 ʋ* ʋ CO ~ ~ ʋ=0 ʋ CO ʋ* ʋ CO +ʋ* “Shift Effect” of Iso-Butoxy Radical r CO

Duschinsky Mixing The excited state PES is (i) displaced, (ii) distorted, (iii) but not rotated relative to the ground state. The excited state PES is (i) displaced, (ii) distorted, and (iii) rotated relative to the ground state. Christian W. Müller, Josh J. Newby, Ching-Ping Liu, Chirantha P. Rodrigo and Timothy S. Zwier, Phys. Chem. Chem. Phys., 2010,12, Vibrational modes Q 1 ’’ and Q 2 ’’ of the ground electronic state are mixed in the excited state (Q 1 ’ and Q 2 ’)

LIF and DF Spectra of 2-Methyl-1-Butoxy Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, J. Phys. Chem. A, , wavenumber/cm -1 H 2 CO A B 14 * Photolysis Laser n= ? ?

15 Comparison of Experimental DF Spectra and FCF Simulation * Photolysis Laser Mozhayskiy, V. A.; Krylov, A. I. ezSpectrum. Transition

16 V= V= A 0 ( cm -1 ) B 0 ( cm -1 ) C ( cm -1 ) LIF Spectrum of Iso-Pentoxy Bath temp. Backing press C 80 psi -5 0 C 80 psi -5 0 C 250 psi 64 cm cm -1

17 * Photolysis Laser DF Spectrum: Type (I) Pumped LIF band:

18 * Photolysis Laser n= DF Spectra: Type (II)

19 * Photolysis Laser DF Spectra: Type (III)

20 Comparison of Experimental DF Spectra and FCF Simulation * Photolysis Laser Mozhayskiy, V. A.; Krylov, A. I. ezSpectrum. Transition

Conclusions: Future Work: Conclusions and Future Work  DF spectra of iso-butoxy, 2-methyl-1-butoxy, and iso-pentoxy radicals were experimentally obtained by pumping different LIF bands.  The vibrational structures of DF spectra suggest existence of multiple conformers under the jet-cooled conditions.  When origin and CO stretch bands are pumped, the DF spectra are dominated by CO stretch progression.  When non-CO stretch vibrational bands are pumped, the DF spectra are dominated by progression of combination bands of CO stretch and pumped modes.  DF spectra of branched chain alkoxy radicals provide vibrational structures of nearly degenerate and states. 21  Rotationally resolved spectra and rotational simulation will help conformational and vibrational assignment of LIF bands.  Quantum chemical calculation of and state potential energy surfaces and vibrational structure. Iso-butoxy2-methyl-1-butoxyIso-pentoxy C1C1 CsType (I)Type (II)Type (I)Type (II)Type (III) (cm -1 ) N/A349252

Acknowledgements Funding: Current Group Members: Former Members: Dr. Neil Reilly UMass Boston 22