Infrared spectra of OCS-C6H6, OCS-C6H6-He, and OCS-C6H6-Ne van der Waals complexes

The infrared spectrum of weakly bound OCS-C6H6 is studied in the region of the nu(1) fundamental band of OCS (similar to 2050 cm(-1)) using a tunable diode laser spectrometer to probe a pulsed supersonic jet expansion. This is one of the first direct infrared observations of a benzene-containing van der Waals complex. A very simple band is observed, corresponding to the parallel transition of a symmetric top. It is shifted by -11.1 cm(-1) with respect to the free OCS monomer. The isotopologues OCS-C-13 (C5H6)-C-12 and OC S-34-C6H6 are observed, and the derived structure has OCS located along the benzene C-6 symmetry axis in an S-bonded configuration with a center of mass separation of 4.42 angstrom, in good agreement with previous microwave spectra. Similar bands are observed for the trimers OCS-C6H6-He and OCS-C6H6-Ne, whose structure is obtained by adding an on-axis rare gas atom to the other side of the benzene. However, the analogous band for OCS-C6H6-Ar is not detected, raising the possibility that the stable form of this trimer may not have the same symmetrical structure. A "mystery" feature is observed close to the OCS-C6H6 band origin and its possible assignment to a cluster such as OCS-(C6H6)(3) is discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3430571]