The OCS (HCCH)2 van der Waals complex: ab initio predictions for the geometry and dynamics

MP2/cc-pVXZ and MP2/aug-cc-pVXZ (X=D, T, Q) complete basis set extrapolation calculations were carried out on the four minimum energy structures located on the potential energy surface of the OCS (HCCH)2 van der Waals complex. The trimer structure consists of an averaged structure representing the dynamical interconversion between two equivalent forms with the (HCCH)2 face adopting a T-shaped conformation. The transition structure is a energetically close-lying geometry with a near-parallel disposition of the two HCCH fragments.