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Global fit analysis Global fit analysis including including 9 9 + + 44 44 hot hot
band of ethane: band of ethane: Evidence of interaction Evidence of interaction with the with the 12 12 fundamentalfundamental
J.R. Cooper and N. Moazzen-Ahmadi
University of Calgary
Ethane is often used as benchmark molecules to Ethane is often used as benchmark molecules to investigate torsion around C-C bond. Its investigate torsion around C-C bond. Its significance lies in the fact that much more significance lies in the fact that much more complex molecules that occur in biological complex molecules that occur in biological environments undergo similar internal motions and environments undergo similar internal motions and insight obtained in mechanisms responsible for insight obtained in mechanisms responsible for internal rotation in ethane will be useful in internal rotation in ethane will be useful in understanding the corresponding effects occurring understanding the corresponding effects occurring in complex biological systems.in complex biological systems.
N6-methyl adenine: modification of DNA structure by the addition of methyl groups (black) affects protein:DNA interactions and so can control gene expression.
ImportanceImportance
ImportanceImportance
The C-H stretching vibrations are used The C-H stretching vibrations are used to monitor ethane in the Earth's to monitor ethane in the Earth's atmosphere.atmosphere.
The lowest frequency vibrational The lowest frequency vibrational fundamental (12 fundamental (12 µµm) has been used to m) has been used to determine the abundance of ethane in determine the abundance of ethane in the atmospheres of Jupiter, Saturn, the atmospheres of Jupiter, Saturn, Titan, Neptune and comets.Titan, Neptune and comets.
Importance of hindered internal rotationImportance of hindered internal rotation
Hindered internal rotation is a Hindered internal rotation is a very very low-frequency vibrational mode low-frequency vibrational mode and strongly anharmonic.and strongly anharmonic.
Ground vibrationalstate
Excited vibrationalstate
• Bath states State mixing IVR
Torsionalsublevels
260.25 260.50 260.75 261.00
WAVENUMBER /cm-1
TRA
NS
MIT
TAN
CE
0.90
0.92
0.94
0.96
0.98
1.00
0.92
0.94
0.96
0.98
1.00
287.9 288.0 288.1 288.2 288.3 288.4 288.5 288.6 288.7
WAVENUMBER / cm-1
TRA
NS
MIT
TAN
CE
0.70
0.80
0.90
1.00
0.80
0.90
1.00
*
**
** ** s
r rs
r
srs
rs
rsr ssr
Torsion
TORSIONAL ANGLE
0
200
400
600
800
1000
1200
cm
-1
N. Moazzen-Ahmadi et al., Journal of molecular spectroscopy (2001).
0
200
400
600
800
1000
1200
1400
cm
-1
v4 = 1
v4 = 0
V9 = 1
3
2
1
0
Methyl rock
gs
The The 99 fundamental fundamental
0
200
400
600
800
1000
1200
1400
cm
-1
High overtone bandHigh overtone band v4 = 1
v4 = 0
V9 = 1
3
2
1
0
34
gs
0
200
400
600
800
1000
1200
1400
cm
-1
V9 = 1
3
2
1
0
34
gs
Methyl rock
Two-band analysisTwo-band analysis
0
1
N. Moazzen-Ahmadi et al., Journal of chemical physics (1999).
843.5 843.6 843.7 843.8 843.9 844.0
cm-1
TR
AN
SM
ITT
AN
CE
rQ8
0.00
0.20
0.40
0.60
0.80
1.00
0.20
0.40
0.60
0.80
1.00
827.18 827.28 827.38 827.48 827.58 827.68
cm-1
TR
AN
SM
ITT
AN
CE
0.00
0.20
0.40
0.60
0.80
1.00
0.20
0.40
0.60
0.80
1.00
rQ2
** *
801.22 801.32 801.42 801.52 801.62 801.72
cm-1
TR
AN
SM
ITT
AN
CE
pQ8
0.00
0.20
0.40
0.60
0.80
1.00
0.20
0.40
0.60
0.80
1.00
738.50 738.65 738.80 738.95 739.10
cm-1
TR
AN
SM
ITT
AN
CE
0.80
0.90
1.00
0.90
1.00
pP12(39)pP15(34)
pP18(29)
pP19(27)
pP9(44)
P18(28)
*
pP21(24)
0.4 Torr, 2 m, -140 C, 0.0024 cm-1
0
500
1000
1500
cm
-1
0
1
2
3
4
gs
N. Moazzen-Ahmadi Journal of molecular spectroscopy (2001).
0
1
V9= 1
0
1
V3= 1
Three-band analysisThree-band analysis
C-C stretching fundamentalC-C stretching fundamentalCH3CH3CH3CH3
993 994 995
WAVENUMBERS
(a)
(b)
(c)
A. Al-Kahtani et al. JCP 98, 101 (1993).
0
500
1000
1500
cm
-1
0
1
2
3
4
gs
N. Moazzen-Ahmadi Journal of molecular spectroscopy (2001).
0
1
V9= 1
0
1
V3= 1
9 9 + + 4 4 4 4 bandband