SCF PERTURBATION-THEORY FOR UNIMOLECULAR REACTIONS

A CNDO/2 SCF perturbation theory is presented for interpreting the form of CNDO/2 potential energy surfaces of unimolecular reactions. The analysis is performed by calculating the energy change Δ E arising from a distortion of the molecular geometry along the reaction coordinate. Δ E is decomposed into different perturbational contributions which are appropriate for an interpretation of the perturbation energy Δ E. Moreover, Δ E is resolved into energy parts arising from a single occupied orbital and contributions due to pairwise orbital interactions. In this way one evaluates numerically how the form of the occupied and unoccupied orbitals determines the magnitude of Δ E. If the distortion occurs along a definite symmetry coordinate, group-theoretical arguments can be applied to discuss the magnitude of characteristic components of the perturbation energy. The SCF perturbation theory is used to analyze the isomerization of ethylene, cis-2-butene and cis-2-butenenitrile. © 1979 Springer-Verlag.