Post on 17-Jan-2016
transcript
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Courtesy of P. Houston & J. Bowman, unpublished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