The Ethylene-Carbon Dioxide Complex and the Double Rotor Model.

The infrared spectrum of the weakly bound CH-CO complex is investigated in the region of the ν fundamental band of CO (≈2350 cm), using a tunable OPO laser source to probe a pulsed supersonic slit jet expansion. The spacing of the various -subbands in this perpendicular (Δ = ±1) spectrum is very irregular, and the pattern of irregularity is quite different from that observed previously in another CH-CO band by Bemish et al. [ 1995 , 103 , 7788 ]. But by allowing for the different symmetry of the ν (CO) upper vibrational state, both results can be strikingly well explained using the "double internal rotor" model as described by Bemish et al.