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

Previous Experimental Studies CO2-CO Dimer Previous Experimental Studies a C2v Symmetry CO stretch 2148.2417(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.

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.

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

Isomer 1 Revisited Experiment Simulated Dimer Trot = 2.5 K

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

Molecular Parameters for CO2-CO and Isotopologue 12C18O2 Isomer 1 Isomer 1 * Isomer 2 Isomer 2 * ν0 2148.2417 2148.2578 2140.2900 2140.2826 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

Observed Combination Bands of Isomer 1 Experiment CO ν1(a1) + out-of-plane rock(b1) c-type Simulation ν0 = 2192.199 cm-1 Experiment CO ν1(a1) + in-plane bend(b2) b-type ν0 = 2172.584 cm-1 Simulation

Observed Combination Bands of Isomer 2 Experiment CO ν1(a1) + out-of-plane rock(b1) c-type Simulation ν0 = 2162.968 cm-1 Experiment CO ν1(a1) + in-plane bend(b2) b-type Simulation ν0 = 2154.483 cm-1

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.

A-Type Coriolis Coupling Isomer 2  Ground state Excited state fundamental Excited state b-type combination Excited state c-type combination 0   2140.2900(2) 2154.4839(2) 2162.9680(2) A 0.397196(57) 0.397198(97) 0.358868(27) 0.435513(82) B 0.074509(26) 0.074443(26) 0.076248(10) 0.074908(13) C 0.062060(12) 0.062031(12) 0.062577(8) 0.063375(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

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

He-CO2-CO Trimer (tentatively)

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

Optimization Calculation Gaussian09 MP2 level CC-PVTZ basis set Parameters Experimental Calculated ν0 2150.5898 A 0.0508 0.0511 B 0.0483 0.0493 C 0.0294 0.0304 units in cm-1