| Résumé | Extensive infrared spectra of the weakly-bound CO₂-CO dimer are observed in the carbon dioxide ν₃ asymmetric stretch region (≈2350 cm⁻¹) using a tunable infrared OPO laser source to probe a pulsed slit jet supersonic expansion. Both C-bonded and O-bonded isomers are analysed for the normal isotopologue as well as for ¹³CO₂-CO and ¹⁶O¹³C¹⁸O-CO, the latter being the first observation of an asymmetrically substituted form for which all values of Ka are allowed. Combination bands involving the lowest in-plane intermolecular bending modes are also studied for both isomers. Weak bands near 2337 cm⁻¹ are assigned to CO₂ hot band transitions (v1, vˡ²₂, v₃) = (01¹1) ← (01¹0), yielding the splitting of the degenerate CO₂ ν₂ bend into in-plane and out-of-plane components due to the presence of the CO. This splitting has rather different values for the C- and O- bonded isomers, 4.57 and 1.59 cm⁻¹, respectively, with the out-of-plane mode higher in energy than the in-plane for both cases. |
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