The gas-phase reactions of O(3P) with perhalogenated butenes: Absolute rate constants and temperature dependences

The temperature dependences of the gas-phase reactions of O(3P) atoms with CF3CFCFCF3, CF3CFCClCF3 and CF3CClCClCF3 were studied under pseudo-first-order conditions in the range 298–359 K, using the discharge flow-chemiluminescence technique. The Arrhenius expressions obtained (in units of cm3 molecule−1 s−1) were: k1 = (0.32 ± 0.05) × 10−12 exp[−(8.1 ± 0.5) × 103/RT], k2 = (1.50 ± 0.74) × 10−11 exp[−(17.7 ± 1.4) × 103/RT] and k3 = (2.58 ± 1.10) × 10−11 exp[−(18.0 ± 1.2) × 103/RT], with Ea in J mol−1. The positive temperature dependences point to the importance of the irreversibility of the addition channel. Complete substitution by halogen atoms in the alkenes results in dramatic reduction of the rate constants. The reactivity trend with the ionization potential is also analyzed.