Kinetic Stability Governs Relative Fullerene Isomer Abundance
Talitha M. Selby, Jasper R. Clarkson, H. Daniel Lee, and Timothy S. Zwier Isomer Specific...
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Transcript of Talitha M. Selby, Jasper R. Clarkson, H. Daniel Lee, and Timothy S. Zwier Isomer Specific...
Talitha M. Selby, Jasper R. Clarkson, H. Daniel Lee, and Timothy S. Zwier
Isomer Specific Spectroscopy and Conformational Energetics of ortho-, meta-,
and para-Ethynylstyrenes60th Annual International Symposium on Molecular Spectroscopy
Funding by DOE
Diane Mitchell, James A. J. Fitzpatrick, and David W. Pratt
J. Phys. Chem. A, 2005, 109, 4484
Introduction: EthynylstyrenesI. Structural-Isomer Specific Spectroscopy
C4H2* +
Robinson, A. G.; Winter, P. R.; Zwier, T. S. J. Phys. Chem. A 2002, 106, 5789.
II. Conformational-Isomer Specific Spectroscopy and Dynamics
?
Ea=?
E=?
Ea=?
E=?
C10H8
cistranscistrans
ortho meta
orthometa para
Techniques
Resonance enhanced two photon ionization (R2PI)
Ultraviolet holeburning spectroscopy (UV HB)
Light Sources
UV: Nd:YAG pumped dye lasers (285-310 nm) and fourth harmonic (266 nm) of Nd:YAG
Ionization continuum
1CR2PI
Ionization continuum
S1
S0
2CR2PI
S1
S0
UV HB
S1
Ionization continuum
hb (10 Hz)probe (20 Hz) tuned
S0 (v=0)
Boltzmann distributionof the vibrational
population prior toexpansion Collisional
cooling to zero-point vibrational
level
B*
B*
B*CE
B*
C
CB
A
D
A
CA
ABC C
AAE BBB B
B D UV
C
A
Boltzmann distributionof the vibrational
population prior toexpansion Collisional
cooling to zero-point vibrational
level
B*
B*
B*CE
B*
C
CB
A
D
A
CA
ABC C
AAE BBB B
B D UV
C
A
Supersonic-jet Spectroscopy
Overview R2PI Spectra of the Ethynylstyrenes
Inte
nsity
(arb
itrar
y un
its)
3520034800344003400033600332003280032400
Wavenumbers (cm-1
)
000
2910(6b1
0)251
0(110)
3210
3110(6a1
0)
3010
2010(131
0)191
0(1310)
321000
0
3110(6a1
0)
2410(121
0)
3010(6a1
0)
2610(1
10) 201
0(1310)
2810(6b1
0)
a) pES
b) mES
c) oES
000(A)
000(B)
Inte
nsity
(arb
itrar
y un
its)
3520034800344003400033600332003280032400
Wavenumbers (cm-1
)
000
2910(6b1
0)251
0(110)
3210
3110(6a1
0)
3010
2010(131
0)191
0(1310)
321000
0
3110(6a1
0)
2410(121
0)
3010(6a1
0)
2610(1
10) 201
0(1310)
2810(6b1
0)
a) pES
b) mES
c) oES
000(A)
000(B)
1CR2PI
2CR2PI
2CR2PI
000(?)
000(?)
000
Ionization Potentials: pES below 8.29 eV | mES 8.48 eV | oES 8.53-8.93 eV
UV Holeburning Spectrum of ortho-Ethynylstyrene
Only trans-oES present
cis-oES only 5% RT population
E=1.8 kcal/mol
E=2.03 kcal/mol
E=0.0 kcal/mol
3440034200340003380033600334003320033000328003260032400
Inte
nsit
y (a
rbit
rary
uni
ts)
Wavenumbers(cm-1)
Para 00
0impurity
000
2CR2PI ortho
UVHB ortho
B3LYP/6-31+G*
c-oES has 1600 cm-1 internal energy pre-expansion
kisomerization (1600 cm-1) ~1011 s-1
kcollision early in expansion ~109-107 s-1
Rate of isomerization faster than collision rate.
UVHB Spectra of meta-Ethynylstyrenes
0.00 kcal/mol
Ea≈1200 cm-1
*B3LYP/6-31+G* level of theory
0.08 kcal/mol
B3LYP/6-31+G*
34400342003400033800336003340033200330003280032600
Wavenumbers/(cm-1)
Inte
nsit
y (a
rbit
rary
uni
ts)
A B
A(000)
B(000)
a) 2CR2PI mES
b) UVHB mES(A)
c) UVHB mES(B)
B3LYP/6-31+G*
Rotationally Resolved Fluorescence Excitation
Experimental
Simulations
32,673.232,670.5
32,672.5932,672.44Wavenumber/cm-1
Experimental
Simulations
32,673.232,670.5
32,672.5932,672.44Wavenumber/cm-1
-0.62685.2(2)982.6(2)2261(2)Experimental
′′
679.7C′′ (MHz)973.4B′′ (MHz)2252A′′ (MHz)Calc c-mESParameter
a/b hybrid423.60.3(2)-0.61679.1(2)979.4(2)2217(2)-0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′
C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
653.4833.23027Calc t-mES
-0.62685.2(2)982.6(2)2261(2)Experimental
′′
679.7C′′ (MHz)973.4B′′ (MHz)2252A′′ (MHz)Calc c-mESParameter
a/b hybrid423.60.3(2)-0.61679.1(2)979.4(2)2217(2)-0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′
C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
653.4833.23027Calc t-mES
~90% a-type
-0.62685.2(2)982.6(2)2261(2)Experimental
′′
679.7C′′ (MHz)973.4B′′ (MHz)2252A′′ (MHz)Calc c-mESParameter
a/b hybrid423.60.3(2)-0.61679.1(2)979.4(2)2217(2)-0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′
C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
653.4833.23027Calc t-mES
-0.62685.2(2)982.6(2)2261(2)Experimental
′′
679.7C′′ (MHz)973.4B′′ (MHz)2252A′′ (MHz)Calc c-mESParameter
a/b hybrid423.60.3(2)-0.61679.1(2)979.4(2)2217(2)-0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′
C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
653.4833.23027Calc t-mES
~90% a-typea-type transitions
B3LYP/6-31+G*
red-shifted conformer of mES b
a
b
a
b
a
b
a
TDM: ~90% A type
mES (A)
Rotationally Resolved Fluorescence Excitation
Simulations
Experimental
33,408.233,405.5
33,406.6433,406.54Wavenumber/cm-1
Simulations
Experimental
33,408.233,405.5
33,406.6433,406.54Wavenumber/cm-1
a-type transitions
pES(000)
-0.96621.5(2)709.2(2)5030(2)Experimental
′′617.7C′′ (MHz)703.3B′′ (MHz)5009A′′ (MHz)CalculatedParameter
a/b hybrid424.60.5(3)-0.96615.6(2)705.7(2)4847(2)0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
-0.96621.5(2)709.2(2)5030(2)Experimental
′′617.7C′′ (MHz)703.3B′′ (MHz)5009A′′ (MHz)CalculatedParameter
a/b hybrid424.60.5(3)-0.96615.6(2)705.7(2)4847(2)0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
-0.96621.5(2)709.2(2)5030(2)Experimental
′′617.7C′′ (MHz)703.3B′′ (MHz)5009A′′ (MHz)CalculatedParameter
a/b hybrid424.60.5(3)-0.96615.6(2)705.7(2)4847(2)0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
*Ground state geometry at B3LYP/6-31+G* level of theory.
-0.96621.5(2)709.2(2)5030(2)Experimental
′′617.7C′′ (MHz)703.3B′′ (MHz)5009A′′ (MHz)CalculatedParameter
a/b hybrid424.60.5(3)-0.96615.6(2)705.7(2)4847(2)0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
-0.96621.5(2)709.2(2)5030(2)Experimental
′′617.7C′′ (MHz)703.3B′′ (MHz)5009A′′ (MHz)CalculatedParameter
a/b hybrid424.60.5(3)-0.96615.6(2)705.7(2)4847(2)0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
-0.96621.5(2)709.2(2)5030(2)Experimental
′′617.7C′′ (MHz)703.3B′′ (MHz)5009A′′ (MHz)CalculatedParameter
a/b hybrid424.60.5(3)-0.96615.6(2)705.7(2)4847(2)0.1(2)
band typefwhm (MHz)OMC (MHz)I′ (amu Å2)′C′ (MHz)B′ (MHz)A′ (MHz)I′′ (amu Å2)
*Ground state geometry at B3LYP/6-31+G* level of theory.
~90% a-type
a
b
a
b
TDM: ~90% A type
pES
B3LYP/6-31+G*
Stimulated Emission Pumping –Population Transfer Spectroscopy
II. UV
Pum
p, pum
p
V. U
V P
robe, probe
III. UV
Dum
p,
dump
IV. C
ollisional
Cooling,
isomerization
kisom
kcool
kcool
Dian, B. C.; Clarkson, J. R.; Zwier, T. S. Science 2004, 303, 1169.
A(v=0)
A*
B(v=0)
000(A) 00
0(B)A*
Expt’l protocol:1. Cool2. Pump3. Dump4. Re-cool5. Probe
Population transfer spectroscopy: Fix Pump on A, Probe on B; Tune Dump: Watch population come into B from A
AB
AABB A
AAA BBB B
A B
BB B
A*A*
AA*A
BA
AB
BA
AB
BB
B
Boltzmann distribution of conformers in the
pre-expansiongas mixture
UV Pump,Dump
UV probe
SEP excites single conformation
Collisional cooling to zero-point
vibrational level
New conformer distribution
detected by UV
Initial Cooling in Expansion
B B
AB
AABB A
AAA BBB B
A B
BB B
A*A*
AA*A
BA
AB
BA
AB
BB
B
Boltzmann distribution of conformers in the
pre-expansiongas mixture
UV Pump,Dump
UV probe
SEP excites single conformation
Collisional cooling to zero-point
vibrational level
New conformer distribution
detected by UV
Initial Cooling in Expansion
B B
I. CoolingPrepare ground state A with a well defined amount of energy
1300120011001000
upper bound (1070 cm
-1)
lower bound
(990 cm-1)
upper bound (1065 cm
-1)
lower bound
(989 cm-1)
a)
b)
c)
d)
Wavenumbers above ZPL (cm-1)
1300120011001000
upper bound (1070 cm
-1)
lower bound
(990 cm-1)
upper bound (1065 cm
-1)
lower bound
(989 cm-1)
1300120011001000 1300120011001000
upper bound (1070 cm
-1)
lower bound
(990 cm-1)
upper bound (1065 cm
-1)
lower bound
(989 cm-1)
a)
b)
c)
d)
Wavenumbers above ZPL (cm-1)
cis-ortho trans-ortho cis-meta trans-meta para cis-ortho trans-ortho cis-meta trans-meta para
a) SEP of cis-meta
d) SEP-PTS trans cis
b) SEP-PTS cis trans
cis-ortho trans-ortho cis-meta trans-meta para cis-ortho trans-ortho cis-meta trans-meta para
SEP and SEP-PTS of mES
c) SEP of trans -meta
Near-threshold population transfer intensity determined by the competition
between isomerization, cooling
kisom(E)
kcool(E)
cis-ortho trans-ortho cis-meta trans-meta para cis-ortho trans-ortho cis-meta trans-meta para
Harmonic RRKM estimate: At threshold, kisom(E) = 2.6X109 sec-1 and kcoll = 1.0X109 sec-1
cis-ortho trans-ortho cis-meta trans-meta para cis-ortho trans-ortho cis-meta trans-meta para
Bounds on the barrier and relative energies of minima
Compound Relative Energy (cm-1) Exp Calc c-m-ethynylstyrene -75 -81a +29c t-m-ethynylstyrene 0a 0c Barrier to cis-trans isomerization (cm-1) Exp Calc m-ethynylstyrene 990-1070a 1237c Styrene 1070±8b 1350c
cis-ortho trans-ortho cis-meta trans-meta para cis-ortho trans-ortho cis-meta trans-meta para cis-ortho trans-ortho cis-meta trans-meta para cis-ortho trans-ortho cis-meta trans-meta para
B A
E(A→B)E(B→A)
E=E(A→B) - E(B→A)
Hollas, J. M.; Musa, H.; Ridley, T.; Turner, P. H.; Weisenberger, K. H.; Fawcett, V. J. Mol. Spectrosc. 1982, 94, 437
Comparison of Methods
•Also gives the form of the entire potential energy function along the torsional coordinate.
•Requires spectroscopic detection of the torsional energy levels
•Assumes the torsional coordinate is the only coordinate involved in isomerization
Torsional Potential Fitting
Comparison of Methods
•Also gives the form of the entire potential energy function along the torsional coordinate.
•Requires spectroscopic detection of the torsional energy levels
•Assumes the torsional coordinate is the only coordinate involved in isomerization
•Not reliant on assignment of normal mode to reaction coordinate
•Relies on the spacing of the SEP transitions, but yes/no question
•Relies on isomerization occurring on a time scale that can successfully compete with collisional cooling
•Apply to cases where many conformers: Breaks into specific A→B pairs
Torsional Potential Fitting
Comparison of Methods
SEP-PTS
Summary of the Ethynylstyrenes
• Only one isomer of oES was observed in the expansion. From calculated energy differences the observed conformer was assigned to the trans conformer.
• Two isomers of mES were observed. The red-shifted conformer was identified as the cis conformer from the rotationally resolved fluorescence excitation spectrum.
• The barrier to cis→trans isomerization in mES is ~1000 cm-1 and the two conformations are nearly isoenergetic, in qualitative agreement with calculations
Acknowledgments
Prof. Timothy S. Zwier The Zwier Group
-Jasper R. ClarksonH. Daniel Lee
Funding: Department of Energy
Prof. David W. PrattThe Pratt Group
-Diane Mitchell-James A. J. Fitzpatrick
UVHB spectrum of trans-ortho-Ethynylstyrene
Evidence of vibronic coupling
•Intensity of transitions
•No overtones
•False origin
Wavenumbers(cm-1)
3440034200340003380033600334003320033000328003260032400
3010(20)1
0
Inte
nsit
y (a
rbit
rary
uni
ts)
000
3110
2010
3010
3110(20)1
0
No 3120 or 302
0
Wavenumbers(cm-1)
3440034200340003380033600334003320033000328003260032400
3010(20)1
0
Inte
nsit
y (a
rbit
rary
uni
ts)
000
3110
2010
3010
3110(20)1
0
No 3120 or 302
0
S0
S1(A′)
S2(A′)
small oscillator strength
coupled by a′vibrations
large oscillator strength
S1(A′)←S0(A′)
Nature of the S0-S1 Transitions:
Transition Dipole Moment Directions
a
b
a a
a
a
aa
a
a b
styrene and phenylacetylene
divinylbenzenes
ethynylstyrenes
diethynylbenzenes
a
b
a a
a
a
aa
a
a b
styrene and phenylacetylene
divinylbenzenes
ethynylstyrenes
diethynylbenzenes
The direction of the TDM in disubstituted benzenes depends both on the nature of the substituents and their relative positions.
•All the meta disubstituted benzenes shown have the TDM along the a-axis.
•In para disubstituted benzenes it appears the nature of the substituents does matter for the TDM direction.
•In pES, the vinyl group has a larger influence on the transitionT.V. Nguyen, J.W. Ribblett, and D.W. Pratt, Chem. Phys 283,279,2002
J.A. Stearns and T.Z. Zwier, J Phys Chem. A, 107,10723,2003
Ribblett, J. W.; Borst, D. R.; Pratt, D. W. J. Chem. Phys. 1999, 111, 8454.Stearns, J. A.; Zwier, T. S. J. Phys. Chem. A 2003, 107, 107117
Wavenumbers(cm-1)
diethynylbenzenes
ethynylstyrenes
divinylbenzenes
360003500034000330003200031000
styrene
phenylacetylene
Wavenumbers(cm-1)
diethynylbenzenes
ethynylstyrenes
divinylbenzenes
360003500034000330003200031000 360003500034000330003200031000
styrene
phenylacetylene
Electronic Origin Shifts in Vinyl and Ethynyl Substituted Benzenes
•Electronic origin shifts are additive
•Trends in ortho, meta, para
• Trends in cis and trans mDVB and mES
•As substituents become closer together they further red shift
T.V. Nguyen, J.W. Ribblett, and D.W. Pratt, Chem. Phys 283,279,2002
J.A. Stearns and T.Z. Zwier, J Phys Chem. A, 107,10723,2003
J.A. Syage, F. Al Adel, and A.H. Zewail, Chem Phys Lett. 103,15,1983
K. Narayanan, G.C. Chang, K.C. Shieh, C.C. Tung, and W.B. Tzeng, Spectochim Acta A. 52,1703,1996