Potential Energy Surface for the Chlorine Atom Reaction with Ethylene: A Theoretical Study

The potential energy surface of the reaction between chlorine atom and ethylene was explored at the MP2/6-31G(d,p), Becke3LYP/6-31G(d,p), QCISD/6-31G(d,p), MP2/6-311+G(d,p), MP2/6-311++G(3df,3pd), and MP2/aug-cc-pVDZ levels of theory. Further QCISD(T)/6-31G(d,p) and QCISD(T)/cc-pVDZ optimizations were performed for some structures of special interest. The geometrical parameters computed for the different structures located on the potential energy surface do not differ too much when employing different methods and basis sets with the only exceptions of those structures involving long distance interactions (van der Waals structures). The pronounced flatness of the potential energy surface in the regions where these structures appear seems to be the responsible for the observed discrepancies. The full optimized QCISD structures tend to become less stable than those computed at the MP2 level, whereas the opposite is true for the Becke3LYP structures. At the MP2 and QCISD levels, the transition structure assoc...