ultraviolet photodissociation dynamics of the 3-cyclohexenyl radical michael lucas, yanlin liu,...
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Ultraviolet Photodissociation Dynamics of the 3-Cyclohexenyl
Radical
Michael Lucas, Yanlin Liu, Jasmine Minor, Raquel Bryant, Jingsong Zhang
Department of Chemistry
University of California, Riverside
69th International Symposium on Molecular Spectroscopy
6/17/2014
Cyclohexyenl Radical
Cycloalkanes are important component of conventional fuels
Cyclohexane model cycloalkane Major producer of benzene
Previous Research: cyclohexyl, phenyl What effect does the double bond have on the
photochemistry?
0
10
20
30
40
50
60
70
0.0
47.14
62.25
47.0947.09
Ene
rgy
(kca
l/mol
)
+ H
+ H
+ H30.0
11.0
+ H
Potential Energy Diagram of c-C6H9
~~
●
●
●
K. Furukawa et al. Int. J. Chem. Kin. 6 (1974) 337NIST Chemistry WebBook
High-n Rydberg H-atom Time-of-Flight (HRTOF)
H
Lyman-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 (1990) 7027
3-chlorocyclohexene3-bromocyclohexene
H-atom TOF Spectra check precursors
244 nm
Inte
nsit
y (a
rb. u
nits
) 3-chlorocyclohexene244 nm
10 30 50 70 90 110 130 150
3-bromocyclohexene
Inte
nsit
y (a
rb. u
nits
)
Time of Flight (s)
H-atom Product Action Spectrum compare with absorption spectrum
R. Schuler et al. Chem. Phys. Lett. 27 (1974) 369; D. Pratt et al. J. Am. Chem. Soc. 96 (1974) 5588
220 230 240 250 260 270 280
This work Schuler et al. Pratt et al.
In
tens
ity (
arb.
uni
ts)
Wavelength (nm)
CM Product Translational Energy Distribution
0 10 20 30 40 50 60 70 80
P
(ET)
CM Translational Energy (kcal/mol)
+ H
+ H
+ H
250 nm
Average ET Release
230 235 240 245 250 255 260 2650.0
0.2
0.4
0.6
0.8
1.0
Ave
rage
f T
Wavelength (nm)
H-atom Product Angular DistributionE
v
q
0 20 40 60 80 100-1
0
1
2
Ani
sotr
opy
Para
met
er
Time of Flight (s)
244 nm
10 30 50 70 90 110 130 150
Inte
nsity
(ar
b. u
nits
)
Time of Flight (s)
= 0o
= 90o
244 nm
Major: β ~ 0Isotropic distributionDissociation time slower than 1 rotational period (ps)
Minor: β < 0Anisotropic distributionDissociation time faster than 1 rotational period
*
0
10
20
30
40
50
60
70
0.0
47.14
62.25
47.0947.09
Ene
rgy
(kca
l/mol
)
+ H
+ H
+ H30.0
11.0
+ H
Photodissociation Mechanism
~~
●
●
●
Repulsive dissociation
I.C. UnimolecularDissociation
Summary
UV photodissociation dynamics of cyclohexenyl was studied in 232-262 nm for the first time
Observed: cyclohexenyl → cyclohexadiene + H Modest translational energy release, fT ~ 0.15 Two components
Major: Isotropic distribution, β ~ 0 Dissociation mechanism: internal conversion from excited electronic state
followed by unimolecular dissociation on ground electronic state Minor:
Anisotropic distribution, β < 0 Dissociation mechanism: direct dissociation from excite state or repulsive part
of ground state
0 20 40 60 80 100
*
P(E
T)
CM Translational Energy (kcal/mol)
Cyclohexyl C
6H
9 Parallel
C6H
9 Perpendicular
*
Comparison With Cyclohexyl
Comparison With Cyclohexyl
230 235 240 245 250 255 260 2650.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
A
vera
ge f T
Wavelength (nm)
Cyclohexenyl Cyclohexyl
Comparison With Cyclohexyl
Moderate translational energy release
Two component Major
Isotropic distribution Statistical distribution Hot radical dissociation
mechanism
Minor Anisotropic distribution, β < 0 Repulsive dissociation mechanism
Large translational energy release
Anisotropic distribution, β > 0 Non-statistical distribution
Dissociation mechanism: direct dissociation from the excited state and/or on the repulsive part of the ground state (possibly via conical intersection).
Cyclohexenyl Cyclohexyl
Acknowledgements
Prof. Jingsong Zhang
Yanlin Liu
Jasmine Minor Raquel Bryant
Zhang Group