THE MOST STABLE ISOMER OF C4H2-(OCS)2 VAN DER WAALS COMPLEX: THEORY AND EXPERIMENT CONFIRM A STRUCTURE WITH C2 SYMMETRY

We report the infrared spectrum of \chem{C_4H_2}-\chem{(OCS)_2} trimer in the region of the \nub{1} fundamental vibration of the OCS monomer. The van der Waals complexes are generated in a supersonic slit-jet apparatus and probed using a rapid-scan tunable diode laser. Both \chem{C_4H_2}-\chem{(OCS)_2} and \chem{C_4D_2}-\chem{(OCS)_2} are studied. Analysis of their spectra establishes that the trimer has \chem{C_2} symmetry. Theoretical calculations performed to find stationary points on the potential energy surface confirm that the experimental structure is the most stable form of the trimer. The rotational parameters computed using double hybrid functionals are in very good agreement with those obtained from the observed spectra