The rotational spectra of seven isotopes of the CO_2-(OCS)_2 mixed trimer have been assigned using pulsed nozzle FTMW spectroscopy techniques. The structure resembles a distorted triangular cylinder with the three monomers aligned roughly parallel. The trimer may be thought of as a slightly perturbed (OCS)_2 dimer with the CO_2 lying above the dimer and crossed at 12 ° and 20 ° to the axes of the two OCS molecules, respectively. The distance between the carbon atoms on the OCS is 3.757 (9) A. The distance between the carbon on each OCS and the carbon on the CO_2 is 3.574(6) and 3.773(8) A, respectively. The dipole moment components for the trimer are μ_a = 0.40(1) D, μ_b = 0.21(7) D, and μ_c = 0.206(1) D with μ_(total) = 0.50(4) D. The structure and dipole moments are close to those predicted by an interaction model which includes a distributed multipole moment electrostatic contribution and atom-atom terms to describe the dispersion and repulsion interactions.
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