Abstract
Rate coefficients are reported for the gas-phase reaction of hydroxyl (OH) radicals with CH2ClCF2Cl (k1) and CH2ClCF3 (k2) over an extended temperature range. The measurements were performed using a laser photolysis/laser-induced fluorescence (PLP/LIF) technique under slow flow conditions at a total pressure of 740 ± 10 Torr. The lower temperature measurements for k1 were in agreement with previous measurements using different techniques. Prior measurements for k2 using different techniques exhibit significant scatter. The new lower temperature data reported here lie intermediate to the previous measurements. Arrhenius plots of the data exhibit significant curvature and were fit to the expression k(T) = ATB exp(−C/T). A semiempirical fitting approach was used in which A and B were obtained from transition-state theory (TST) and C was determined from a nonlinear least-squares fit to the experimental data. Ab initio calculations were used to evaluate the thermochemical properties of the activated complex. The resulting modified Arrhenius expressions were k1(295−788 K) = (8.53 ± 4.06) × 10-19T2.28±0.18 exp[(−937 ± 296)/T] cm3 molecule-1 s-1 and k2(295−866 K) = (3.06 ± 4.02) × 10-18T1.91±0.03 exp[(−644 ± 313)/T] cm3 molecule-1 s-1. Error limits are ±2σ. The TST-based modified Arrhenius expression is compared to previous TST and SAR predictions. The effect of halogen substitution on the reactivity of these compounds is briefly discussed. The incorporation of a Wigner tunneling factor and its impact on the TST fit of the data is also presented and discussed.
Published Version
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