IR Spectroscopy of Trans-Acrolein:
The n11 Fundamental
n11
and n16 + n18  n18 Hot Band
n16
*
n18
**
Hongyu Shi, Li-Hong Xu, R.M. Lees, D.W. Tokaryk
Centre for Laser, Atomic and Molecular Sciences (CLAMS)
Department of Physics, University of New Brunswick
A.R.W. McKellar
Steacie Institute for Molecular Sciences, NRC
D.R.T. Appadoo
Canadian Light Source, University of Saskatchewan
(Australian Synchrotron Company, Australia)
1
A'
n1
n2
n3
n4
n5
n6
n7
n8
n9
n10
n11
n12
n13
Description
nobs / cm-1
CH2 asym-stretch 3103
CH* stretch
3069
CH2 sym-stretch
2998
CH** stretch
2800
C=O stretch
1742
C=C stretch
1625
CH2 scissors
1420
CH** bend
1360
CH* bend
1275
C-C stretch
1158
CH2 in-plane rock 912
CCO bend
564
CCC bend
324
Vibrational Modes
of Trans-Acrolein
*
**
A"
n14
n15
n16
n17
n18
Description
nobs / cm-1
CH2 twist
993
CH** o-o-p bend 972
CH2 o-o-p wag 959
CH* o-o-p bend 593
C-C torsion
158
Ref. Y. Hamada, Y. Nishimura, M. Tsuboi, Chem. Phys. 100 (1985) 365-375.
2
Energy Diagram:
Fundamentals,
Overtones,
Density of States
Harmonic Approximation
2000
1800
1600
-1
*
Energy (cm )
1400
1200
1000
….
n 14 A" CH2 twist
800
**
n 15 A" CH** o/p
n 16 A" CH2 o/p
n 11 A' CH2 i/p
600
n 17
n 12
n 13
n 18
400
H2C=C(H*)-C(H**)=O
200
0
n18
n13
n12
n17 n11
n 16
n15 n 14
A"
A'
A'
A"
A"
A"
A'
A"
A" CH* o/p
A' CCO bend
A' CCC bend
A" C-C torsion
All
3
McKellar et al, 1, 2, 3, 5-state
treatments below 700 cm-1
700
In the 10 mm region
2n12
1120
4n18
600
2n13
n132n18
2 states
2 states
1100
n17
3 states
1080
7n18
500
3n18
n13n18
2 states
n16+n18 combination
n13n17n18
n11n18
n173n18
n12
5 states
2n133n18
n16n18
n135n18
1060
n12n13n18
n123n18
1040
1020
n15 to be found
(weak, close to 3n13)
400
1000
300
2n18
n13
2 states
980
n14
n14 fundamental
3n13, n15
960
6n18
2n132n18
n16
n134n18
n16 fundamental
n13n17
n11
n172n18
n11 fundamental
940
200
n18
1 state
920
900
100
4
n16, n14 band analysis
NRC II: 180K, 4 x 2m path
CLS III: room T, 4.8 m path
(High-freq. filter)
n11 band analysis
n16 + n18  n18 hot band analysis
920
930
940
950
960
CLS IV: room T, 7.2 m path
970
980
990
1000
5
The n11 CH2 In-Plane Rocking Band (A’ a/b-Type)
a-type Q branches
K
908.0
10
9
908.5
8
909.0
7
6
909.5
910.0
K=6
910.0
910.1
5
4
910.5
K=5
910.1
910.2
910.2
910.3
910.3
910.4
910.4
 a-type Q-branch initial lines have so far been identified up to K = 15
 R and P series followed to high J (> 40)
 assignments confirmed with ground state combination differences
6
Intensity Ratio (est.) from a- and b-Type Subbands
 b-type assignments have been found based on prediction
 From assignments, we learnt a-type transitions are much stronger
than b-type transitions.
- qualitatively
We wish to know approximately what intensity ratio (- quantitatively)
would be between the two types:
(transition dipole moment)a /(transition dipole moment)b.
Partition func.
Vibrational transition dipole moment
and temp. dependence
Line intensity
hcnij
  hcEi m
T0 

Sij  nij
1  e kT e kT
TZv Zr 
Q

2
J ' K '| J " K"
2
Related to population difference
Rotational transition strength
Transition freq.
7
Boltzmann factor
Vibrational Transition Dipole Moment Ratio
of a- and b-Type Transitions in the n11 Band
(Sij_a / Sij_b)calc

(Sij_a / Sij_b)obs 
2
a
∂μ
∂Q
Ka' = 7
n11 = 1
2
b
9
8
7
rR(7)
pP(9)
qR(7)
8
7
6
qP(9)
9
8
7
n11 = 0
Ka" = 6
∂μ
∂Q
10
9
8
Ka" = 8
Ka" = 7
8
Ratio of a-/b- Type Transition Dipole Moment Squared
∂μ
∂Q
6
2
a
∂μ
∂Q
5
2
≈2.4
b
4
3
2
1
0
0
20
40
60
80
100
120
140
160
180
Number of data points
9
n16 Fundament and Hot Bands – Low Resolution Plot
n16 + n18 n18 hot band
centered at ~ 957.6 cm-1
n16 fundamental band
centered at ~ 958.8 cm-1
2
pQ
Ka"
8
935
7
940
6
5
945
3
4
5
6
rQ
Ka"
4
950
955
Transmission / Wavenumber (cm-1)
File # 1 = ACROLEIN-001CM-1_COADDBGSUB
Acrolein in 30cm MP cell with 16 passes
960
965
970
975
980
Paged X-Zoom CURSOR
Res=0.001
10
Q Branches – Medium and High Resolution
973.22
973.24
rQ
pQ
branch of
n16hot band
Ka" = 5
Ka= 6-5 33 32
branch of n 16
fundamental band
Ka" = 5
branch of n14
fundamental band
Ka" = 7
rQ
31 30
973.26
29 28 27 26 25 24 23 22 20 18 16 14 12 … = J
973.28
973.3
973.32
973.34
973.36
973.38
11
Asymmetric Rotor Hamiltonian
H  n vib  AP  BP  CP + higher order
2
a
2
b
2
c
B C 2
 n vib  Bav P   A  Bav  P 
Pb  Pc2
2
+ higher order
2

2
a

E  Evib  Bav J  J  1   A  Bav  K  asym.
2
 J  1   JK J  J  1 K   K K  H J J  J  1
2
2
2
4
6
 H JK J  J  1 K  H KJ J  J  1 K  H K K  ...
 J J
2
2
2
4
3
3
(Isolated band modeling using Maki’s program)
12
Molecular Parameters (cm-1) for Trans-Acrolein
n11
n16
n16+n18
0
157.8839(1) 911.3419(1)
1.57954076 1.5271577(3) 1.552589(10)
0.155424164 0.15564911(3) 0.154799(3)
0.14152-893 0.14208587(3) 0.141265(3)
3.99773
3.947(7)
3.3(22)
0.19342
-0.028(2)
1.90(81)
-0.073(115)
0.229(52)
-0.057(4)
3.47417
3.6226(7)
3.92(21)
-2.92953
-2.851(2)
-4.17(41)
1.20053
-0.2192(3)
-0.322(22)
0.63(14)
-0.041
-61.9(30)
-0.01586
0.0222(7)
1.46(26)
-0.8252(1)
-2.19(18)
3.17(1)
35.2(43)
0.00089
958.74077(11)
1.5967121(97)
0.15529617(78)
0.14152241(81)
4.59(29)
1.027(75)
957.6290(1)
1.543791(10)
0.155274(1)
0.142086(1)
6.68(78)
0.36(16)
0.091(34)
0.044(11)
-0.084(2)
4.07(5)
-1.71(14)
0.905(45)
0.258(30)
-44.8(9)
-2.39(16)
-5.34(72)
216(36)
0.00073
Ground Statea
ni
A
B
C
J
K
hJ
hJK
hK
J
JK
K
HJ
HJK
HKJ
HK
LK
rms
a
x 109
x 106
x 1011
x 108
x 106
x 108
x 107
x 105
x 1011
x 1011
x 109
x 108
x 1012
n18b
3.543(12)
-2.95(13)
2.514(25)
-1.69(67)
-5.757(97)
-1.27(18)
0.0010
M. Winnewisser, G. Winnewisser, T. Honda, E. Hirota, Z. Naturforsch. 30a (1975) 1001-1014.
McKellar, D.R.T. Appadoo, J. Mol. Spectrosc., in press.
b A.R.W.
13
Summary
 Vibrational substates have been identified for the n11 mode of
trans-acrolein from Ka = 0 to 15, and for n16 + n18 from Ka = 0 to
10, generally up to order J ~ 40 for most subbands.
 Asymmetry splitting has been observed for Ka up to 5.
 Assigned transitions have been modeled by a Watson asymmetric
rotor Hamiltonian using the least squares program written by Art
Maki. The two datasets are currently fitted with standard
deviations of 0.00089 and 0.00073 cm-1.
14