Kinetic Study of the Reactions CCl3 + O2 + M -> CCl3O2 + M from 1 to 760 Torr and from 233 to 333 K

Article abstract of DOI:10.1021/j100172a037

The kinetics of reaction 1, CCl3 + O2 + M -> CCl3O2 + M, has been investigated in detail as a function of temperature and over a large pressure range.At low pressure, 0.8-12 Torr, the reaction was investigated by laser photolysis and time-resolved mass spectrometry, while at high pressure (760 Torr), flash photolysis with UV absorption spectrometry was employed.At the low pressure limit, the rate expression, k₁(0) = (1.6 +/- 0.3) x 10^-30(T/298)^-(6.3+/-0.5) cm⁶ molecule^-2 s^-1 (M = N2), exhibits a quite strong negative temperature coefficient.The obtained strong collision rate expression, 7.0 x 10^-30(T/298)^-4.3 cm⁶ molecule^-2 s^-1, using either RRKM calculations or Troe's factorized expression, is unable to reproduce the experimental temperature dependence, unless an unreasonably strong temperature dependence is assigned to the collisional efficiency factor: β_c = 0.23(T/298)^-2.0 (M = N2).Similar results are obtained for other chlorofluoromethyl radicals.The falloff curves were constructed by using RRKM calculations obtained by adjusting β_c and the transition-state model, in order to reproduce the experimental data.The rate expression at the high-pressure limit was derived from these calculations k₁(infinite) = (3.2 +/- 0.7) x 10^-12(T/298)^-(1.2+/-0.4) cm³ molecule^-1 s^-1.All the parameters to be used in Troe's analytical expression for calculating the bimolecular rate constant at any pressure and temperature are given.The rate constant at the low-pressure limit k₁(0) is more than an order of magnitude lower than for the CF3 radical.The RRKM calculations show that this arises from a large difference in the C-C bond dissociation energies in the corresponding peroxy radicals: 81.9 kJ mol^-1 for CCl3O2 instead of ca. 145 kJ mol^-1 for CF3O2.