Absolute rate determinations and temperature dependences of the

PABLO M. COMETTO, MARIANO A. TERUEL*, RAÚL A. TACCONE AND SILVIA I. LANE*

CHEMICAL PHYSICS LETTERS

Elsevier

Año: 2006 vol. 417 p. 480 - 485

0009-2614

  Abstract The rate constants for the gas-phase reactions of ground state oxygen atoms with  CF3CH=CH2 (1), CF3CF=CF2 (2) and CF3CCl=CCl2 (3) have been measured directly using a discharge flow tube employing the O(3P) chemiluminescence titration method. The experiments were carried out under pseudo-first-order conditions with  [O(3P)]0 << [propene]0. The temperature dependences of the reactions were studied for the first time in the range 298-363 K. The Arrhenius expressions obtained (in units of cm3 molecule-1 s-1) were: k1 = (0.28 ± 0.09) x 10-11 exp[-(10.4 ± 0.9) x103 / RT], k2 = (1.57 ± 0.72) x 10-11 exp[-(15.6 ± 1.3) x103 / RT], k3 = (2.23 ± 1.27) x 10-11 exp[-(16.0 ± 1.6) x103 / RT]. All the rate coefficients display a positive temperature dependence which points to the importance of the irreversibility of the addition mechanism for these reactions. Halogen substitution in the alkenes is discussed in terms of reactivity with O(3P) and its relation with the ionization potential.