The OCS trimer: Isotopic studies, structure, and dipole moment

The rotational spectra of ((OCS)-O-18)(3) and ((OCS)-C-13)(3) have been ass igned using a pulsed-nozzle Fourier transform microwave spectrometer. The d ata 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 carbo n atoms form a triangle with the axes of the monomer units roughly parallel to each other (barrel-like structure). The monomers have an antiparallel-l ike arrangement, with the dipole moment of one monomer opposing those of th e ether two monomers. The dipole moment of the complex has been measured, g iving values of mu(a) = 0.537(10) D, mu(c) = 0.373(2) D, and mu(total) = 0. 653(8) D. The b component of the dipole moment was too small to determine f rom 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 molecule s and with the OCS dimer. Semiempirical calculations have been performed on the (OCS)(3) system, and they show good qualitative agreement with the exp erimental structure.