Photodissociation dynamics of 1-propenyl radical Michael Lucas, Yu Song, Jingsong Zhang*, Department of Chemistry University of California, Riverside Riverside, CA Christopher Brazier Department of Chemistry and Biochemistry California State University, Long Beach Long Beach, CA 90840

Photodissociation of Free Radicals Free radicals Open shell Highly reactive Important to many areas of chemistry Combustion, plasma, atmospheric, interstellar Dissociation depends on potential energy surfaces Multiple low-lying electronic states and nonadiabatic processes Provide benchmarks for theory

C3H5C3H5 Combustion Four isomers: allyl, 1-propenyl, 2-propenyl, cyclopropenyl Allyl radical is the smallest  conjugated system with odd number of  electrons. Allyl radical was proposed to be one of the most important precursors for the formation of benzene and other cyclic compounds in the flames. C 3 H 3 + C 3 H 5 → fulvene + H + H H + fulvene → H + benzene

Potential Energy Diagram of C 3 H 5 C.L. Currie et al. J. Chem. Phys. 1966, 45, 488 M. Gasser et al. J. Phys. Chem. A 2010, 114, 4704 H.J. Deyerl et al. J. Chem. Phys. 1999, 110, 1450 S.G. Davis et al. J. Phys. Chem. A 1999, 103, 5889

1-Propenyl Intermediate in allyl dissociation H-atom abstraction product in propene + OH and phenyl reactions Previous Studies Secondary dissociation of 1-bromopropene with 193-nm radiation CH 3 + C 2 H 2 channel was dominant at lower internal energy Propyne + H and isomerization to the allyl radical followed by the dissociation to the allene + H channel opened at higher internal energy M. L. Morton et al. J. Phys. Chem. A 2002, 106, C.-W. Zhou et al. J. Phys. Chem. A 2009, 113, 2372 L.K.Huynh et al. J. Phys. Chem. A 2009, 113, 3177 V.V. Kislov et al. J. Phys. Chem. A 2012, 116, 4176

High-n Rydberg H-atom Time-of-Flight (HRTOF) H Lyman-  Probe nm Photolysis Pulsed Valve Rydberg Probe nm Detector Skimmer 193 nm H transitions 1 2 nH+H+ H (n) H (2 2 P) nm Lyman-  nm K. Welge and co-workers, J Chem Phys 92, 7027 (1990) 1-bromopropene or 1-chloropropene in Ar

H-atom Product Action Spectra

H-atom Product TOF Spectra

CM Product Translation Energy Distribution 232 nm

P(E T ) Calculations Courtesy of P. Houston & J. Bowman, unpublished

Potential Energy Diagram of C 3 H 5 C.L. Currie et al. J. Chem. Phys. 1966, 45, 488 M. Gasser et al. J. Phys. Chem. A 2010, 114, 4704 H.J. Deyerl et al. J. Chem. Phys. 1999, 110, 1450 S.G. Davis et al. J. Phys. Chem. A 1999, 103, 5889

Average E T Release

Angular Distribution β~0 Isotropic distribution Dissociation time is longer than one rotational (> ps) E v 

Pump-Probe Delay Time Dissociation rate ≥ 10 8 s -1 H-atom production from the 1-propenyl radical flight out of the H from interaction region 236 nm

Photodissociation Mechanism C.L. Currie et al. J. Chem. Phys. 1966, 45, 488 M. Gasser et al. J. Phys. Chem. A 2010, 114, 4704 H.J. Deyerl et al. J. Chem. Phys. 1999, 110, 1450 S.G. Davis et al. J. Phys. Chem. A 1999, 103, 5889 I.C. Unimolecular Dissociation Unimolecular Dissociation

Summary Identify the first UV absorption feature in the action spectra = Isotropic angular distribution, β ~ 0 Dissociation time: ps < t ≤ 10 ns Dissociation Mechanism: internal conversion from excited electronic state to ground electronic state followed by unimolecular dissociation on ground state

Acknowledgements Dr. Jingsong Zhang Dr. Yu Song, UC Davis Jessy Lemieux Lydia Plett Paul Jones Mixtli Campos-Pineda Dr. Christopher Brazier, California State University, Long Beach Trajectory calculations Dr. Paul Houston, Georgia Tech Dr. Joel Bowman, Emory University Funding NSF