Transcript OhioStatepresent.ppt

Ultraviolet Cavity Ringdown Spectra of
2-Cyclohexen-1-one and its Inversion
Potential Energy Function
Mohamed Rishard, Emily Giles, Jaeboom Choo,
Daniel Autrey, Stephen Drucker, Jaan Laane
June 20 2005
Outline
• Introduction
• Previous spectroscopic studies on 2-cyclohexen-1-one
(2CHO)
• Cavity ringdown spectra of 2CHO
• Inversion potential energy function of 2CHO in the ground
electronic (S0) state
• Conclusions and present research work
2-Cyclohexen-1-one
O
H
H
Mol. Weight = 96.13 g/mol
1
2
6
H
3
5
H
4
H
Boiling point = 168-1690C (at 1 atm)
Vapor pressure = ~1.8 torr (at 250C)
H
H
H
• An asymmetric six-membered non-planar ring molecule
• Microwave studies by Manley and Tyler in 1970 proposed a
structure which only C-5 was significantly out-of-plane
• The conjugation between C=C and C=O groups is expected to
provide extra rigidity to the ring
Out-of- plane vibrations of 2CHO
(+)O
O
1
O
1
2
6
5
3
4
1
(-)
(-) 2
6
(+)
3
5
(-)
4
(-)
(-)
2
6
5
(+) 3
4
(+)
 39
 38
 37
ring inversion
ring bending
C=C twisting
Previous spectroscopic studies: Vapor
Raman spectra
L. A. Carreira, T.G. Towns, T. B. Malloy, J. Chem. Phys., 70(5), 2273, (1979)
Previous spectroscopic studies: far-IR
spectra
T. L. Smithson, H. Wieser, J. Chem. Phys., 73(5), 2518, (1980)
Previous spectroscopic studies: far-IR
spectra
f
2
4
6
8
9
12

←

i
1
3
5
7
10
11
Observed/cm-1
99.85
99.23
98.63
98.02
97.48
96.87
Obs.- Calc.
0.04
-0.01
-0.02
-0.04
0.02
0.02
Barrier = 3379 ± 43 cm -1
T. L. Smithson, H. Wieser, J. Chem. Phys., 73(5), 2518, (1980)
Cavity Ringdown Spectroscopy-Experimental
Cavity Ring-Down Spectroscopy, Andrew Orr-Ewing, Mike Ashfold
CRDS spectra of 2CHO
S1 ( n,  * )
3910
3910
000 = 26089.1cm -1
S0
Relative wavenumbers of 2CHO with respect
to the S1 band origin (Res. 0.1 cm-1)
Calculated and experimental Raman
spectra of 2CHO
Vibrational assignments of 2CHO
(Frquencies are in cm-1)
Observed by CRDS
Calculateda
Inferred
Assignment
-99.0
103.0
-99.2 b
3910
-197.0
-------
-197.2 b
39 02
-294.9
-------
-294.1 b
39 03
-243.0
240.8
-244 c
3810
-303.2
307.8
-304.1 b
3710
a
From b3lyp/6-311+g(d,p) calculation
b
Inferred from far-IR data
C
From the current vapor Raman spectrum
Vibrational energy levels for the ground
state (S0) of 2CHO
6,7
4,5
2,3
6,7
4,5
2,3
96.9
98.2
VI = 0,1
97.5
98.6
99.8
243.0
303.2
99.0
VI = 0,1
 39
 38
 37
Ring inversion potential
Potential energy function: V = 7.459 x 102 S2 – 2.378 x 103 S4
Barrier to planarity = 1895 ± 300 cm-1
(calculated barrier-to-planarity by DFT methods = 2090 cm-1)
Conclusions and present work
• Previous Raman and IR studies misinterpreted the spectra and
miscalculated the inversion barrier.
• CRDS spectra have allowed us to clarify the vibrational levels of lowfrequency vibrations
• The experimental value of 1895 ± 300 cm-1 for the barrier to planarity
agrees very well with the value of 2090 cm-1 determined by DFT
calculations
• The large uncertainty value came from the extrapolation of the P.E.
function above the experimental values.
• Determination of inversion barriers of S1 and T1 states and also for
the 2,2,6-deuterated isotopomer of 2CHO is currently being carried
out
Acknowledgement$
• National Science Foundation
• Robert A. Welch Foundation
• Texas Advanced Research Program