(OCS)3 van der Waals Complex: A Theoretical Study
journal contributionposted on 23.08.2003, 00:00 by H. Valdés, J. A. Sordo
Ab initio calculations [MP2, MP4SDTQ, and QCISD(T)] using different basis sets [6-31G(d,p), cc-pVXZ (X = D, T, Q), and aug-cc-pVDZ] were carried out to explore the potential energy surface of (OCS)3. Six minimum energy structures were located and characterized. The most stable one corresponds to an antiparallel arrangement of the monomers, in agreement with microwave spectroscopic experiments. The nature of the interactions present in the trimer was analyzed by using the Symmetry Adapted Perturbation Theory. The importance of the induction forces in this type of system suggests that results from semiempirical potentials with no inclusion of this component should be considered with extreme caution. The analysis helps to rationalize the experimentally observed preference for the antiparallel arrangement. Two transition structures corresponding to the interconversion of enantiomeric forms of the parallel and the most stable of the antiparallel arrangements were located on the potential energy surface. The relatively high energy barrier between them is consistent with the very small splittings exhibited by the rotational lines of the microwave spectra.