Rotational spectrum, structure and modeling of an isomer of the HCCH-OCS dimer

A second T-shaped isomer of the HCCH-OCS dimer has been observed by Fourier -transform microwave spectroscopy. This isomer has the OCS monomer interact ing with the triple bond of the acetylene monomer through the sulfur atom, with a calculated center of mass separation, R-CM, of 4.622(2) Angstrom. Th e effects of nuclear spin statistics on the relative intensities of the tra nsitions confirm the C-2v symmetry of the complex. The dipole moment, mu(al pha) = 0.9516(8) D, indicates an induced moment of 0.24 D. The geometry is consistent with results from a semi-empirical model and ab initio calculati ons which suggest that this isomer is higher in energy than the near-parall el HCCH-OCS isomer. (C) 1999 Elsevier Science B.V. All rights reserved.