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

Abstract

The infrared spectrum of weakly bound OCS-C(6)H(6) is studied in the region of the nu(1) fundamental band of OCS ( approximately 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-(13)C (12)C(5)H(6) and OC (34)S-C(6)H(6) 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 A, in good agreement with previous microwave spectra. Similar bands are observed for the trimers OCS-C(6)H(6)-He and OCS-C(6)H(6)-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-C(6)H(6)-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-C(6)H(6) band origin and its possible assignment to a cluster such as OCS-(C(6)H(6))(3) is discussed.