JETCOOLED DISPERSED FLUORESCENCE DF SPECTROSCOPY OF BRANCHED CHAIN

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

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

Introduction and Motivation Ø Alkoxy radicals (RO·) are key intermediates in the oxidation of hydrocarbons both in combustion and in the atmosphere. Ø Reactions of alkoxy radicals in the atmosphere: i) decomposition ii) reaction with O 2 iii) isomerization (via internal H transfer). i) iii) Potential energy profiles (kcal/mol) for the ground state decomposition and isomerization reactions of isobutoxy calculated at the B 3 LYP/6 -311++G(d, p) level of theory. Ø Identification of conformers of alkoxy radicals. Finlayson-Pitts, B. J. ; Pitts, J. N. Chemistry of the Upper and Lower Atmosphere; Academic Press: San Diego, 2000. Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, 2013 117 (50), 13229 -13235 3

Different Conformers of Branched Chain Alkoxy Radicals iso-butoxy 2 -methyl-1 -butoxy iso-pentoxy Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, 2013 117 (50), 13229 -13235 4

iso-butoxy 2 -metyl-1 -butoxy iso-pentoxy 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 B 3 LYP/6 -311++G(d, p) Level of theory. Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, 2013 117 (50), 13229 -13235 5

LIF: laser-induced fluorescence DF: dispersed fluorescence Experimental LIF/DF Setup RONO/He Photolysis Laser Nd: YAG νx 3 Vacuum Chamber Δν~0. 1 cm-1 Doubling Crystal Pulsed Dye Laser νx 2 Nd: YAG Excitation Laser OGC PMT Box. Car Δν~30 cm-1 DF spectrograph i. CCD LIF Computer PMT=photomultiplier tube; OGC=optogalvanic cell i. CCD=intensified charge coupled device 6

LIF and DF Spectra of Iso-Butoxy Radical ? ? H 2 CO Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, The Journal of Physical Chemistry A, 2013 117 (50), 13229 -13235 * Photolysis Laser D (B+248 cm-1) Type (II) C (B+142 cm-1) B (28788 cm-1) Type (I) A (28091 cm-1) 7

Comparison of Experimental DF Spectra and FCF Simulation * Photolysis Laser FCF= Franck-Condon factor Mozhayskiy, V. A. ; Krylov, A. I. ez. Spectrum. http: //iopenshell. usc. edu/downloads. 8

DF Spectra: Type (II) d D (B+248 cm-1) c C (B+142 cm-1) n=0 V=non CO stretch mode 1 2 3 4 5 9

DF Spectrum: Type (I) * Photolysis Laser n=0 1 2 3 4 Mixture of CO stretch & CH 3 torsion Mixture of CH 3 scissor & C-C stretch mode C-C-C umbrella mode A (28091 cm-1) 10

“Shift Effect” of DF Spectra Calculated d c 11

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

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. Vibrational modes Q 1’’ and Q 2’’ of the ground electronic state are mixed in the excited state (Q 1’ and Q 2’) 13 Christian W. Müller, Josh J. Newby, Ching-Ping Liu, Chirantha P. Rodrigo and Timothy S. Zwier, Phys. Chem. Phys. , 2010, 12, 2331 -2343

? LIF and DF Spectra of 2 -Methyl-1 -Butoxy ? H 2 CO A B wavenumber/cm-1 Gaiting Liang, Chengxuan Liu, Haiyan Hao, Lily Zu, and Weihai Fang, J. Phys. Chem. A, 2013 117, 13229 -13235 * Photolysis Laser n=0 1 2 3 4 14

Comparison of Experimental DF Spectra and FCF Simulation * Photolysis Laser Mozhayskiy, V. A. ; Krylov, A. I. ez. Spectrum. http: //iopenshell. usc. edu/downloads. Transition 15

LIF Spectrum of Iso-Pentoxy Bath temp. 220 C -50 C Backing press. 80 psi 250 psi A 0 (28598. 1 cm-1) B 0 (28821. 3 cm-1) C (29058. 1 cm-1) V=0 1 2 3 4 V=0 1 64 cm-1 48 cm-1 2 3 4 5 16

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

DF Spectra: Type (II) * Photolysis Laser n=0 1 2 3 4 5 18

* Photolysis Laser DF Spectra: Type (III) 19

Comparison of Experimental DF Spectra and FCF Simulation * Photolysis Laser Mozhayskiy, V. A. ; Krylov, A. I. ez. Spectrum. http: //iopenshell. usc. edu/downloads. Transition 20

Conclusions and Future Work Conclusions: Ø DF spectra of iso-butoxy, 2 -methyl-1 -butoxy, and iso-pentoxy radicals were experimentally obtained by pumping different LIF bands. Ø The vibrational structures of DF spectra suggest existence of multiple conformers under the jet-cooled conditions. Ø When origin and CO stretch bands are pumped, the DF spectra are dominated by CO stretch progression. Ø When non-CO stretch vibrational bands are pumped, the DF spectra are dominated by progression of combination bands of CO stretch and pumped modes. Ø DF spectra of branched chain alkoxy radicals provide vibrational structures of nearly degenerate and states. (cm-1) Iso-butoxy 2 -methyl-1 -butoxy C 1 Cs Type (I) 426 373 265 Iso-pentoxy Type (II) Type (III) 275 N/A 349 252 Future Work: Ø Rotationally resolved spectra and rotational simulation will help conformational and vibrational assignment of LIF bands. Ø Quantum chemical calculation of vibrational structure. and state potential energy surfaces and 21

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