Observation of a planar isomer of the OCS–(C2H2)2 trimer

Infrared spectra of a new planar isomer of the OCS–(C2H2)2 trimer are observed in the region of the OCS ν1 fundamental band (∼2060 cm−1) using a tunable diode laser to probe a pulsed supersonic slit jet expansion. Three isotopologues are analyzed in detail (16OCS–(HCCH)2, 16OCS–(DCCD)2, and 18OCS–(DCCD)2), while the spectrum of a fourth is found to be heavily perturbed (18OCS–(HCCH)2). Observed rotational constants of planar OCS–(C2H2)2 agree fairly well with previous ab initio calculations, and with previous and present semi-empirical calculations. It should now be possible to assign the microwave spectrum of planar OCS–(C2H2)2.