JETCOOLED LASERINDUCED FLUORESCENCE SPECTROSCOPY OF LARGE SECONDARY ALKOXY

JET-COOLED LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF LARGE SECONDARY ALKOXY RADICALS JINJUN LIU, MING-WEI CHEN, AND TERRY A. MILLER Laser Spectroscopy Facility Department of Chemistry The Ohio State University 06/21/10

Motivation I: Hydrocarbon oxidation * J. J. Orlando, G. S. Tyndall, T. J. Wallington, Chem. Rev. 103, 4657 (2003)

Motivation II: Jahn-Teller and pseudo-Jahn-Teller effects CH 2 DO ethoxy 1 -propoxy …… methoxy CH 3 O CD 3 O CHD 2 O iso-propoxy 2 -butoxy …… * J. Liu et al. , JCP, 130, 074302 (2009). * D. Melnik et al. , JCP, submitted * X. Q. Tan et al. , JCP, 97, 9311 (1993) * J. Liu et al. , 65 th MSS, TG 14 (2010). * S. Gopalakrishnan et al. , JCP, 118, 4954 (2003). * V. Stakhursky et al. , JCP, 125, 094316 (2006)

Motivation III: Conformers of alkoxy radicals For secondary alkoxy radicals, N=3(n-3) N: number of conformers; n: number of carbon atoms. N=3 N=9 N=27 Φ 1=O-C 1 -C 2 -C 3; Φ 2=C 1 -C 2 -C 3 -C 4; Φ 3=C 2 -C 3 -C 4 -C 5 … G+= gauche clockwise (Φ ~ 60 o) T= trans (Φ ~ 180 o) G-= gauche counterclockwise (Φ ~ -60 o)

Experimental apparatus I: Low-resolution LIF PMT Doubling Crystal Vacuum Chamber (SHG) Δν~3 GHz Photolysis Excitation RONO +He/Ne T~1 K

Low-resolution LIF spectra

Low-resolution LIF spectra

Low-resolution LIF spectra

Experimental apparatus II: High-resolution LIF PMT Doubling Crystal Δν~100 MHz Pulse Dye Amplifier Excimer Laser (Xe. Cl) Xe. F Photolysis Laser RONO+He Etalon Box. Car Δν~1 MHz Ar+ Laser Computer CW Ring Dye Laser I 2 Lockin PD PD

High-resolution LIF spectra of 2 -pentoxy Type I: A, C 1, C 2 Type II: B, C 3, D 1 D 2, D 3 Type II (overlapping): D 4, 5 D 6, 7

High-resolution LIF spectra of 2 -hexoxy Type I: A, C 1 Type I (overlapping): C 2, 3 C 4, 5 Type II: B, D

High-resolution LIF spectra 2 -pentoxy 2 -hexoxy Type II

Spectroscopic model ground state (X) excited state (B) Hamiltonian H = HRot + HSR H = HRot = ANa 2 + BNb 2 + CNc 2 HSR = ½ ab (Na. Sb + Sb. Na) a, b molecular constants rotational constants A", B", C" A', B', C' spin-rotation constants* aa", bb", cc" ½( ab" + ba") transition types* ½( ac" + ca") a: b: c ½( bc" + cb") * Predicted based on the experimental results of iso-propoxy.

Quantum chemistry calculations 2 -pentoxy 2 -hexoxy ~ ~ A and X states: B 3 LYP/6 -31+G(d) ~ B state: CIS/6 -31+G(d) * Scaled by 0. 76. [G. Tarczay, S. Gopalakrishnan, and T. A. Miller, J. Mol. Spectrosc. 220, 276 (2003). ]

Simulation with calculated/predicted parameters 2 -pentoxy

Simulation using evolutionary algorithm (EA)* 2 -pentoxy * W. L. Meerts and M. Schmitt Int. Rev. Phys. Chem. , 25(3), 353– 406 (2006)

Fit parameters 2 -pentoxy G+T: from global fit of Bands A, C 1 and C 2 (Type I); TT: from global fit of Bands B and C 3 (Type II). [ ]: discrepancy between cal. and expt. ; ( ): one standard deviation.

Simulation of overlapping bands 2 -pentoxy, Band D 4, 5 (CO stretch band of TT conformer) Frequency interval: δν~0. 03 cm-1 D 3

Low-resolution LIF spectra Origin CO stretch B D + T G + GA B C D CO TCO +T TT G+T GA B C D CO TTCO G+A B C D TT TTT G+TTCO TTTCO +TTT G+TTT TTTT G A B C D CO TTT CO +TTTT G+TTTT TTTTT G A B C D CO TTTT CO TTTTTT TTTTT A B C D CO G+TTTTT G +TTTTTCO TTTTTTT TTTTTT CO A B C D G+TTTTTT G +TTTTTTCO

Summary and Future work High-resolution rotationally resolved spectra of 2 -pentoxy and 2 -hexoxy have been obtained and simulated. n Evolutionary algorithm was used for global fitting successfully. n These spectra were assigned to all-Trans conformers or conformers with a G+ OCCC dihedral angle. 2 -pentoxy: G+T, TT; 2 -hexoxy: G+TT, TTT. n Good agreement between experimentally determined and calculated/predicted parameters has been found. n n n Quantitative understanding of the pseudo-Jahn-Teller effect in secondary alkoxy radicals; Study of cyclic alkoxy radicals.

Acknowledgements Miller Group Prof. Dr. W. Leo Meerts Radboud University Nijmegen The Netherlands Thank you all!