Ab initio chemical kinetics for reactions of ClO with Cl ₂ O ₂ isomers

The mechanisms for the reactions of ClO with ClOClO, ClOOCl, and ClClO ₂ have been investigated at the CCSD(T)/6-311+G(3df)PW91PW91/6- 311+G(3df) level of theory. The rate constants for their low energy channels have been calculated by statistical theory. The results show that the main products for the reaction of ClO with ClOClO are ClOCl + ClOO, which can be produced readily by ClO abstracting the terminal O atom from ClOClO. This process occurs without an intrinsic barrier, with the predicted rate constant: k (ClO + ClOClO) = 7.26 × 10 ^-10 T ^-0.15 ×exp (-40/T) cm ³ molecule ^-1 s ^-1 for 200-1500 K. For the reactions of ClO + ClOOCl and ClClO ₂ , the lowest abstraction barriers are 7.2 and 7.3 kcalmol, respectively, suggesting that these two reactions are kinetically unimportant in the Earths stratosphere as their rate constants are less than 10 ^-14 cm ³ molecule ^-1 s ^-1 below 700 K. At T=200-1500 K, the computed rate constants can be represented by k (ClO + ClOOCl) = 1.11 × 10 ^-14 T ^0.87 exp (-3576/T) and k (ClO + ClClO ₂ ) 4.61 × 10 ^-14 T ^0.53 exp (-3588/T) cm ³ molecule ^-1 s ^-1 . For these systems, no experimental or theoretical kinetic data are available for comparison.