The OCS Trimer: Isotopic Studies, Structure, and Dipole Moment

Abstract

The rotational spectra of (18OCS)3 and (O13CS)3 have been assigned using a pulsed-nozzle Fourier transform microwave spectrometer. The data for these isotopic species have been combined with normal species data from a paper by Connelly et al. [Connelly, J. P., et al. Mol Phys. 1996, 88, 915] to determine the nine structural parameters of the trimer. The carbon atoms form a triangle with the axes of the monomer units roughly parallel to each other (barrel-like structure). The monomers have an antiparallel-like arrangement, with the dipole moment of one monomer opposing those of the other two monomers. The dipole moment of the complex has been measured, giving values of μa = 0.537(10) D, μc = 0.373(2) D, and μtotal = 0.653(8) D. The b component of the dipole moment was too small to determine from our data but is predicted to be about 0.02 D. The structure of (OCS)3 has been compared with similar trimers involving linear triatomic molecules and with the OCS dimer. Semiempirical calculations have been performed on the (OCS)3 system, and they show good qualitative agreement with the experimental structure.