Computational Studies of the Bimolecular Reaction Dynamics of the C2H4 + F2 System

Article abstract of DOI:10.1021/j100312a031

The bimolecular reaction dynamics of C2H4 + F2 on a previously described potential energy surface have been investigated by using quasi-classical trajectory methods.All important reaction channels are open on this potential surface, and the calculated equilibrium geometries, reaction exothermicities and fundamental vibration frequencies are in fair-to-good accord with measured values.The major reaction products are found to be either CH2CH2F + F or CH2=CHF + HF. 1,2-Difluoroethane is found as a reaction intermediate leading to CH2=CHF + HF but is never observed as a final product.The calculated reaction cross sections are all less than 5 Angstroem² even for translational energies more than 1 eV in excess of the reaction threshold.Almost all of the reaction exothermicity is partitioned into the internal modes of CH2CH2F or CH2=CHF.Very little of this energy appears as relative translational motion of the products.HF is usually formed in the ν = 0, 1, or 2 vibrational state.The calculated center-of-mass differential cross section for fluorine atom scattering shows a strong backward component along with an isotropic component.The first of these is shown to arise from a direct reaction mechanism; the second is the result of complex formation.Formation of fluoroethylene is shown to occur via a complex mechanism involving formation of 1,2-difluoroethane as an intermediate.The calculated thermal rate coefficients for CH2CH2F and CH2=CHF formation are 1.38E14*exp<-13600/RT> and 1.90E13*exp<-11040/RT> cm³/(mol*s), respectively.There is some suggestion of mode-specific rate enhancement for the reaction leading to CH2CH2F but not for the formation of CH2=CHF.In the first case, the C-H stretching modes are found to be the most effective in enhancing the rate.The results are compared and contrasted with gas-phase data reported by Kapralova et al. and with the matrix isolation results obtained by Frei et al.