LAUSR

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 (v 1, , v 3) = (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. GRAPHICAL ABSTRACT