The reaction of pentadienyl radicals (C 5 H 7 ) with O 2 has been studied by a combination of pulsed laser photolysis and photoionization mass spectrometry. These radicals were generated either by the photolysis of 1,3-pentadiene or by a two step process, photolyzing carbon tetrachloride to form Cl atoms, which then abstracted a hydrogen atom from 1,4-pentadiene. The equilibrium between pentadienyl radicals, O 2 and pentadienylperoxy radicals could be observed over the temperature range 268-308 K. An analysis of the time-dependent signal of pentadienyl radicals was used to evaluate the equilibrium constant. From the temperature dependence of the equilibrium constant, the enthalpy change for the reaction C 5 H 7 + O 2 f C 5 H 7 O 2 was found to be 56 ( 5 kJ mol -1 . The C-O bond energy in the C 5 H 7 -O 2 adduct is weaker than those of allyl-type peroxy radicals. Possible values of the heats of formation of C 5 H 7 and C 5 H 7 -O 2 radicals and the resonance stabilization energy of the C 5 H 7 radical are discussed.

Isobutane pyrolysis is studied in an unpacked Pyrex reactor at 20–100 torr initial pressures and 750–793 K. Results are interpreted in terms of a long chain radical mechanism and the reaction is modeled. The reaction selectivity or ratio of the initial production rate of isobutene (or hydrogen) to that of propene (or methane) is practically given by the ratio of the rate constant of abstraction of a tertiary hydrogen atom of isobutane to that of a primary one. A sensitivity analysis clearly shows that self‐inhibition is essentially due to methylallyl radicals produced by hydrogen abstraction from isobutene. The model has been manually adjusted to experimental results and most of the adjusted rate constants are in agreement with literature data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 425–437, 1998

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The pyrolysis of isobutane has been studied a t 500°C in a "Pyrex" static reactor packed with platinum. It is shown that both dehydrogenation and demethanation rates are strongly depressed by the metal packing. The reaction rates are very sensitive to the amount of cabonaceous coating which is deposited on the walls. As this amount increases, both rates first increase, go through a maximum and decrease. These observations are compared with those previously made on propane pyrolysis in a "Pyrex" reactor packed with stainless steel. The present results are interpreted on the basis of a hetero-homogeneous chain mechanism in which the selectivity of the free-radical reaction is not altered referring to the unpacked reactor. 0

Isobutane pyrolysis has been studied in the presence of oxygen at about in 773 K unpacked and in PbO-coated packed Pyrex reactors. The reaction is shown to be accelerated by oxygen in reactors of low surface-to-volume ratio and strongly inhibited in packed PbOcoated reactors. These oxygen effects are explained in terms of interaction between two radical chain systems, one of pyrolysis, the other of oxidation. Oxygen introduces additional chain initiations and a degenerate chain branching step due to H 2 O 2 while oxygenated radicals are efficiently removed at the reactor wall. All experimental results have been modeled and many rate constants of elementary steps were evaluated. The collision efficiency of radicals on HO 2ў a PbO-coated Pyrex surface has been determined in the temperature range of this study. ᭧