Infrared spectra of both isomers of CO${}_2$-CO in the CO${}_2$ ${\nu }_3$ region

Abstract

Extensive infrared spectra of the weakly-bound CO${}_2$-CO dimer are observed in the carbon dioxide ${\nu }_3$ 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 analyzed for the normal isotopologue as well as for 13CO${}_2$-CO and ${}^{16}$O${}^{13}$C${}^{18}$O-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 CO${}_2$ hot band transitions (v1, v2l2, v3) = (0111) <-- (0110), yielding the splitting of the degenerate CO${}_2$ ${\nu }_2$ 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, 4.56 and 1.59 cm-1, respectively, with the out-of-plane mode higher in energy than the in-plane for both cases.

26 pages, 5 figures and 5 tables