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The kinetics of the reaction of methyl radicals with oxygen atoms has been investigated in a heatable tubular reactor coupled to a photoionization mass spectrometer. The reactants (CH3 and 0(3P)) were generated homogeneously in the reactor by the simultaneous in situ photolysis of acetone and S02. Initial conditions were always chosen to yield [O]/[CH3]0 > 20. The decay of CH3 was monitored as a function of [O] to yield rate constants for the reaction O + CH3 -* H2CO + H at five temperatures between 294 and 900 K. The rate constant was found to be independent of temperature, having a value 1.4 X 10-10 cm3 molecule-1 s-1, and also independent of density in the range used in this study, (3-24) X 1016 molecule cm-3. The mechanism was verified by direct observations of H2CO production. The new experimental method, which can be used to investigate many reactions of oxygen atoms with free radicals, is described in detail.

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Using the relative kinetic method, rate coefficients have been determined for the gas-phase reactions of chlorine atoms with propane, n-butane, and isobutane at total pressure of 100 Torr and the temperature range of 295-469 K. The Cl 2 photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm 3 molecule −1 s −1 ) have been derived: (7.4 ± 0.2) × 10 −11 exp [−(70 ± 11)/T], Cl + C 3 H 8 → HCl + CH 3 CH 2 CH 2 ; (5.1 ± 0.5) × 10 −11 exp[(104 ± 32)/T], Cl + C 3 H 8 → HCl + CH 3 CHCH 3 ; (7.3 ± 0.2) × 10 −11 exp[−(68 ± 10)/T], Cl + n-C 4 H 10 → HCl + CH 3 CH 2 CH 2 CH 2 ; (9.9 ± 2.2) × 10 −11 exp[(106 ± 75)/T], Cl + n-C 4 H 10 → HCl + CH 3 CH 2 CHCH 3 ; (13.0 ± 1.8) × 10 −11 exp[−(104 ± 50)/T], Cl + i -C 4 H 10 → HCl + CH 3 CHCH 3 CH 2 ; (2.9 ± 0.5) × 10 −11 exp[(155 ± 58)/T], Cl + i -C 4 H 10 → HCl + CH 3 CCH 3 CH 3 (all error bars are ±2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule.