Rotational Spectrum and Structure of the Carbonyl Sulfide−Trifluoromethane Weakly Bound Dimer

Pure rotational spectra of five isotopomers of the 1:1 weakly bound complex formed between carbonyl sulfide
and trifluoromethane (TFM) have been measured using Fourier transform microwave spectroscopy. The
experimental rotational constants and dipole moment components are consistent with a structure of Cs symmetry
in which the dipole moment vectors of OCS and HCF3 are aligned antiparallel and at an angle of about 40°
and with a center of mass separation of 3.965(26) Å. The derived H···O distance is 2.90(5) Å, which is up
to 0.6 Å longer than is seen in other similar TFM complexes exhibiting C−H···O interactions. Ab initio
calculations at the MP2/6-311++G(2d,2p) level give a structure with rotational constants that are in reasonable
agreement with those of the normal isotopic species.