National Research Council of Canada. Security and Disruptive Technologies
Infrared spectra of the CO₂─CO dimer are observed in the carbon monoxide CO stretch region (≈2150 cm⁻¹). Combination bands yield the first experimental determinations of intermolecular mode frequencies for the planar T-shaped C-bonded form (‘isomer 1’): 24.34 cm ⁻¹ for the in-plane CO rock and 43.96 cm ⁻¹ for the out-of-plane CO rock. These values are significantly higher than the analogous modes of the O-bonded form (‘isomer 2’), previously determined to be 14.19 and 22.68 cm ⁻¹, respectively. New results are also reported for both isomers of the¹²C¹⁸O₂-substituted form of the dimer. Weak ‘satellite bands’ observed for both isomers are tentatively assigned to the trimer He─CO₂─CO.