1. High Resolution Infrared Spectroscopy of the CO2-CO Dimers and (CO2)2-CO Trimer
A.J. Barclay, S. Sheybani-Deloui, N. Moazzen-Ahmadi
Department of Physics and Astronomy, University of Calgary
K. H. Michaelian
Natural Resources Canada
CANMET Energy
A.R.W. McKellar
Steacie Institute of Molecular Sciences
National Research Council of Canada

2. Previous Experimental Studies
CO2-CO Dimer
Previous Experimental Studies a
C2v Symmetry
CO stretch
(1) cm-1
R = 3.91 Å b
Microwave/Infrared Study : A.C. Legon, A.P. Suckley, J. Chem. Phys. 91 (1989) 4440.
Infrared Study B.J. Howard, et al., J. Chem. Soc. Faraday Trans. 86 (1990) 1943.
Infrared Study : A.R.W. McKellar, et al., J. Mol. Spectrosc. 179 (1996) 345.

3. CO-CO2 Dimer “Isomer 2” Binding Energies (MP2 level) Calculated†
BSSE Corrected
Isomer 1
429.9
410.6
256.6
Isomer 2
306.3
308.9
100.2
Isomer 1
units in cm-1
Isomer 2
ab initio : † Z.-H. Cao and Y.-X. Bu, Chem. J. Chinese Universities 19, 94 (2003).
ab initio : ‡ M. Venayagamoorthy, T.A. Ford, J. Mol. Struct: THEOCHEM 717 (2005) 111.

4. Experimental Conditions
Pulsed supersonic slit jet apparatus
Daylight Solutions quantum cascade laser
Expansion mixture:
0.2% CO
0.2% CO2
Helium carrier gas
9 atm backing pressure
Frequency Calibration:
N2O reference
Fixed etalon
PGOPHER

5. Isomer 1 Revisited
Experiment
Simulated
Dimer
Trot = 2.5 K

6. Observation of Isomer 2 New band at 2140.29 cm-1
2.98 cm-1 below the CO monomer origin
Qualitatively similar to Isomer 1
15-20% increase in B and C
R = 3.58 Å
Experiment
Simulation

7. Molecular Parameters for CO2-CO and Isotopologue 12C18O2
Isomer 1
Isomer 1 *
Isomer 2
Isomer 2 * ν0 A
0.3957
0.3516
0.3972
0.3530 B
0.0628
0.0609
0.0745
0.0722 C
0.0538
0.0515
0.0621
0.0593
units in cm-1
* Denoting 12C18O2 substituted dimer

8. Observed Combination Bands of Isomer 1
Experiment
CO ν1(a1) + out-of-plane rock(b1) c-type
Simulation
ν0 = cm-1
Experiment
CO ν1(a1) + in-plane bend(b2) b-type
ν0 = cm-1
Simulation

9. Observed Combination Bands of Isomer 2
Experiment
CO ν1(a1) + out-of-plane rock(b1) c-type
Simulation
ν0 = cm-1
Experiment
CO ν1(a1) + in-plane bend(b2) b-type
Simulation
ν0 = cm-1

10. Observed and Calculated Intermolecular Frequencies
Isomer 1
Observed
Observed*
Calculated†
Calculated‡
b-type, in-plane
24.343
20.1
24.30
c-type, out-of-plane
43.958
43.997
44.9
42.81
Isomer 2
Observed
Observed*
Calculated†
Calculated‡
b-type, in-plane
14.194
13.945
19.0
15.45
c-type, out-of-plane
22.676
22.673
38.2
36.32
*12C18O2 substituted form
units in cm-1
† Z.-H. Cao and Y.-X. Bu, Chem. J. Chinese Universities 19, 94 (2003).
‡ M. Venayagamoorthy, T.A. Ford, J. Mol. Struct: THEOCHEM 717 (2005) 111.

11. A-Type Coriolis Coupling
Isomer 2 
Ground state
Excited state fundamental
Excited state b-type combination
Excited state c-type combination 0
(2)
(2)
(2) A
(57)
(97)
(27)
(82) B
(26)
(26)
(10)
(13) C
(12)
(12)
(8)
(11)
units in cm-1
Interaction Parameter
Coriolis Constant
Isomer 1
0.13 cm-1
0.17
Isomer 2
0.575 cm-1
0.72

12. “Satellite Bands” Isomer 2 Isomer 1 Experiment Simulated Dimer
Simulated Trimer

13. He-CO2-CO Trimer (tentatively)

14. (CO2)2-CO Trimer Higher side of isomer 1 fundamental 2150.58976 cm-1
Experiment
Band Origin
Higher side of isomer 1 fundamental
cm-1
b-type band
C2 symmetry (pin wheel structure)
Simulation

15. Optimization Calculation
Gaussian09
MP2 level
CC-PVTZ basis set
Parameters
Experimental
Calculated ν0 A
0.0508
0.0511 B
0.0483
0.0493 C
0.0294
0.0304
units in cm-1