Transcript OSU Conference M Lucas.pptx

Photodissociation dynamics of
1-propenyl radical
Michael Lucas, Yu Song, Jingsong Zhang*,
Department of Chemistry
University of California, Riverside
Riverside, CA 92521
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
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
Potential Energy Diagram of C3H5
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
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
Previous Studies
Secondary 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
High-n Rydberg H-atom Time-of-Flight
(HRTOF)
Detector
H+
n
H (n)
2
366.2 nm H (22P)
121.6 nm
Lyman-a
H
1
H transitions
Pulsed Valve
Skimmer
1-bromopropene or
1-chloropropene in
Ar
K. Welge and co-workers, J Chem Phys 92, 7027 (1990)
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Courtesy of P. Houston & J. Bowman, unpublished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, 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 ET Release
Angular Distribution
v
q
E
β~0
Isotropic distribution
Dissociation time is longer
than one rotational (> ps)
Pump-Probe Delay Time
H-atom production from the 1-propenyl radical
236 nm
flight out of the H from interaction region
Dissociation rate
≥ 108 s-1
Photodissociation Mechanism
Unimolecular
Dissociation
I.C.
I.C.
Unimolecular
Dissociation
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
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
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