Abstract: The reaction path of the reaction C₂H²⁺+ H₂→C₂H³⁺+Hhas been traced by Fukui's theory of intrinsic reaction coordinate by using an ab initio MO method with the gradient technique. Furthermore, the dynamical properties along the reaction path and CVT rate constants with correction of tunneling effect and effect of curvature have been investigated by reaction path Hamiltonian theory and variational transition state theory. On this basis,the enhancement of rate constant by vibrational excitation of C-C stretching mode has beencalculated. The calculated vibrational enhancement is of the same order of magnitude with the experimentally estimated value.

Key words: Ab initio calculation, Variational transition state, Molecular reaction dynamics, Vibrational-state-selected rate constant