Fundamental and torsional combination bands of two isomers of the OCS-CO2 complex in the CO2 ν3 region.

Spectra of two isomers of the weakly bound complex OCS-CO2 are observed in the region of the CO2 ν3 fundamental vibration (∼2349 cm(-1)), using an infrared tunable diode laser to probe a pulsed supersonic slit-jet expansion. Two bands are measured and analyzed for each isomer, the fundamental asymmetric stretch of the CO2 component and a combination band involving this fundamental plus the intermolecular out-of-plane torsional mode. For one isomer, the corresponding torsional combination band is also detected in the OCS ν1 stretching region (∼2060 cm(-1)). The resulting torsional frequencies are found to be 18.8 and 15.9 cm(-1) for isomers a and b of OCS-CO2, respectively. This may be the first time that such a combination band is observed for a higher-energy isomer of a weakly bound complex.