Kinetics of the Reactions of Chlorinated Very Short-Lived Substances (VSLSs) with Chlorine Atoms

Chlorinated very short-lived substances (VSLSs), which are not controlled by the Montreal Protocol, are of current concern with regard to recovery of stratospheric ozone. Further study is needed on the temperature dependences of chlorinated VSLSs relevant to atmospheric conditions. Here, the kinetics of chlorinated VSLSs, such as chloroform (CHCl₃), dichloromethane (CH₂Cl₂), dichloroethane (CH₂ClCH₂Cl), and trichloroethene (C₂HCl₃) reacting with chlorine atoms, were investigated between 180 and 400 K, expanding the range of temperatures relative to previous studies. RRKM/Master Equation and Canonical Variational Transition State Theory were utilized to calculate the rate coefficients using the MultiWell suite of programs. CCSD(T), QCISD(T), and M062X with aug-cc-pV(T+d)Z levels of theory were used to calculate the kinetic parameters. Arrhenius equations obtained from fits to the calculated rate coefficients are k₁ = (2.66 ± 0.7) × 10^-12 exp [(-927 ± 131)/T] cm³ molecule^-1 s^-1, k₂ = (8.99 ± 0.3) × 10^-12 exp [(-957 ± 19)/T] cm³ molecule^-1 s^-1, k₃ = (1.51 ± 0.16) × 10^-11 exp [(-714 ± 54)/T] cm³ molecule^-1 s^-1, and k₄ = (9.17 ± 1.8) × 10^-12 exp [(612 ± 101)/T] cm³ molecule^-1 s^-1 for the reactions of CHCl₃, CH₂Cl₂, CH₂ClCH₂Cl, and C₂HCl₃ with Cl atoms, respectively. The rate coefficients for the reactions of chlorinated VSLSs with Cl atoms from this study are compared with the most recent recommended values from the NASA/JPL and IUPAC evaluations and with literature values. The reactivity trends of the reactions are discussed.