Infrared spectra of the OCS trimer

Infrared spectra of the barrel-shaped trimer (OCS)(3), previously known from its microwave spectrum, are reported for the first time. The observations are carried out in a supersonic slit-jet expansion of a He+OCS gas mixture which is probed with a tunable diode laser. Three rotationally resolved bands associated with the nu(1) fundamental vibration of OCS (2062.20 cm(-1)) are observed, at about 2047, 2053, and 2077 cm(-1). Small perturbations are noted in the 2077 cm(-1) band and may also be present in the 2053 cm(-1) band, which is weak and hence more difficult to analyze precisely. Employing a variety of evidence, we suggest a plausible assignment for the nature of the OCS vibrations in each of the three bands.