Kinetics of the reactions of O(P-3) with CCl2=CH2, (Z)-CHCl=CHCl, and CCl2=CCl2: A temperature dependence study

摘要

Absolute rate coefficients for the gas-phase reactions of ground-state oxygen atoms with CCl2=CH2 (1), (Z)-CHCl=CHCl (2) and CCl2=CCl2 (3) have been measured directly using the fast flow discharge technique. The experiments were carried out under pseudo-first-order conditions with [O(P-3)](0) [chloroethene](0). The temperature dependences of the reactions of O(3P) with CCl2=CH2, (Z)-CHCl=CHCl and CCl2=CCl2 were studied in the range 298-359 K. The kinetic data obtained were used to derive the following Arrhenius expressions (in units of cm(3) molecule(-1) s(-1)): k(1) = (1.82 +/- 1.29) x 10(-11) exp[-(12.63 +/- 0.97) x 10(3)/RT], k(2) = (1.56 +/- 0.92) x 10(-11) exp[-(16.68 +/- 1.54) x 10(3)/RT], k(3) = (4.63 +/- 1.38) x 10(-11) exp[-(19.59 +/- 3.21) x 10(3)/RT]. This is the first temperature dependence study of the reactions of O(P-3) atoms with (Z)-CHCl=CHCl and CCl2=CCl2. All the rate coefficients display a positive temperature dependence and pressure independence, which points to the importance of the irreversibility of the addition mechanism for these reactions. The obtained rate coefficients are compared with previous studies carried out mainly at room temperature. The rates of addition of O atoms and OH radicals to the double bond of alkenes at 298 K are related by the expression: log k(OH) = 0.57278 log k(O(3P)) - 4.095. A correlation is presented between the reactivity of chloroethenes toward O atoms and the second-order perturbational term of the frontier molecular orbital theory which carries the contribution of the different atomic orbitals to the HOMO of the chloroethene. To a first approximation, this correlation allows room-temperature rate coefficients to be predicted within +/- 25-30% of the measured values.