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 interacting with the triple bond of the acetylene monomer through the sulfur atom, with a calculated center of mass separation, RCM, of 4.622(2) Å. The effects of nuclear spin statistics on the relative intensities of the transitions confirm the C2v symmetry of the complex. The dipole moment, μa=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 calculations which suggest that this isomer is higher in energy than the near-parallel HCCH–OCS isomer.