Infrared spectra of a new planar isomer of the OCS-(C2H2)(2) trimer are observed in the region of the OCS nu(1) fundamental band (similar to 2060 cm(-1)) using a tunable diode laser to probe a pulsed supersonic slit jet expansion. Three isotopologues are analyzed in detail ((OCS)-O-16-(HCCH)(2), (OCS)-O-16-(DCCD)(2), and (OCS)-O-18-(DCCD)(2)), while the spectrum of a fourth is found to be heavily perturbed ((OCS)-O-18-(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). (C) 2011 Elsevier B.V. All rights reserved.