Abstract
The rotational spectra for seven isotopomers of the OCS–OCS–C
2H
4 trimer have been observed with a Fourier transform microwave spectrometer. Their moments of inertia were fitted to a structure in which the plane of the ethylene is roughly parallel to a plane formed by the OCS monomers aligned with parallel dipoles. Dipole moment measurements and semi-empirical modeling confirmed this geometry. The transitions were split into doublets separated by 30–100
kHz by a tunneling motion in the complex. Isotopic studies indicated that this motion involved rotation of the ethylene in its molecular plane. The structure of the trimer is very similar to the HCCH–(OCS)
2 trimer in which the dipoles of the two OCS monomers were also aligned parallel. The complex is compared with several dimers containing ethylene which also show tunneling motions.