Geometric Isomerism in the OCS−CS₂ Complex: Observation of a Cross-Shaped Isomer

Infrared spectra of the OCS−CS2 van der Waals complex were studied in a pulsed supersonic slit-jet using a tunable diode laser probe. Spectra were recorded in the region of ν1 fundamental of OCS. Two bands were observed and analyzed, one band corresponding to a previously observed planar isomer and another due to a new isomer which has a nonplanar cross-shaped structure. The intermolecular (center of mass) separation of the planar isomer is 3.87017(2) Å. The structure of this isomer has been determined previously from its rotational spectrum. The cross-shaped isomer was observed here for the first time, and its structure was determined with the help of isotopic substitution. Two structural parameters, the intermolecular distance (R) and an angle (ϕ), are necessary to completely define the structure. These were determined to be R 3.5553(8) Å and ϕ = 104.82(22)° which are in fair agreement with the theoretical predictions.