Photodissociation dynamics of1-propenyl radical

Michael Lucas, Yu Song, Jingsong Zhang*,Department of Chemistry

University of California, Riverside

Riverside, CA 92521

Christopher BrazierDepartment of Chemistry and Biochemistry

California State University, Long Beach

Long Beach, CA 90840

Photodissociation of Free Radicals

Free radicalsOpen shell

Highly reactive

Important to many areas of chemistryCombustion, plasma, atmospheric, interstellar

Dissociation depends on potential energy surfacesMultiple low-lying electronic states and nonadiabatic processes

Provide benchmarks for theory

C3H5

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.

C3H3 + C3H5 → fulvene + H + H

H + fulvene → H + benzene

H H

H

H H

Potential Energy Diagram of C3H5

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

1-PropenylIntermediate in allyl dissociation

H-atom abstraction product in propene + OH and phenyl reactions

Previous StudiesSecondary dissociation of 1-bromopropene with 193-nm radiation

CH3 + C2H2 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, 10831

H

HH

H

HC.-W. Zhou et al. J. Phys. Chem. A 2009, 113, 2372L.K.Huynh et al. J. Phys. Chem. A 2009, 113, 3177V.V. Kislov et al. J. Phys. Chem. A 2012, 116, 4176

High-n Rydberg H-atom Time-of-Flight (HRTOF)

HLyman

-a Probe

121.6 nm

Photolysis

Pulsed Valve

Rydberg Probe

366.2 nm

Detector

Skimmer

193

nm

H transitions

1

2

n H+

H (n)

H (22P)

121.6 nmLyman-a

366.2 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(ET) Calculations

Courtesy of P. Houston & J. Bowman, unpublished

Potential Energy Diagram of C3H5

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

Average ET Release

Angular Distribution

β~0

Isotropic distribution

Dissociation time is longer than one rotational (> ps)

E

v

q

Pump-Probe Delay Time

Dissociation rate ≥ 108 s-1

H-atom production from the 1-propenyl radical

flight out of the H from interaction region236 nm

Photodissociation Mechanism

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

I.C. I.C.

UnimolecularDissociation

UnimolecularDissociation

Summary

Identify the first UV absorption feature in the action spectra

<fT> = 0.125-0.14

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

AcknowledgementsDr. 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