Ab initio chemical kinetic study on the reactions of ClO with C ₂H₂ and C₂H₄

The mechanisms for the reactions of ClO with C₂H₂ and C₂H₄ have been investigated at the CCSD(T)/CBS level of theory. The results show that in both systems, the interaction between the Cl atom of the ClO radical and the triple and double bonds of C₂H ₂ and C₂H₄ forms prereaction van der Waals complexes with the O-Cl bond pointing perpendicularly toward the π-bonds, both with 2.1 kcal/mol binding energies. The mechanism is similar to those of the HO-C₂H₂/C₂H₄ systems. The rate constants for the low energy channels have been predicted by statistical theory. For the reaction of ClO and C₂H₂, the main channels are the production of CH₂CO + Cl (k_1a) and CHCO + HCl (k _1b), with k_1a = 1.19 × 10^-15T ^1.18 exp(-5814/T) and k_1b = 6.94 × 10^-21 × T^2.60 exp(-6587/T) cm³ molecule^-1 s^-1. For the ClO + C₂H₄ reaction, the main pathway leads to C₂H₄O + Cl (k_2a) with the predicted rate constant k_2a = 2.13 × 10^-17T ^1.52 exp(-3849/T) in the temperature range of 300-3000 K. These rate constants are pressure-independent below 100 atm.