KINETICS OF THE CHCL2 AND CH2CL ASSOCIATION REACTIONS WITH MOLECULAR-OXYGEN BETWEEN 298-K AND 448-K AND FROM 1 TO 760 TORR OF TOTAL PRESSURE

The rate constants for the recombination reactions between molecular oxygen and the halogenated methyl radicals CHCl2 and CH2Cl were determined over the pressure range of 1 to 760 Torr in nitrogen as a function of temperature. The CHCl2 + O2 reaction (1) was studied over the temperature range 298 < T/K < 383 and the CH2Cl reaction (2) over the range 298 < T/K < 448. The large range in pressure was attained by using two complementary techniques: Low-pressure experiments (1-10 Torr) were concluded using laser photolysis/photoionization mass spectrometry. High-pressure experiments (20-760 Torr) were carried out with the laser photolysis/UV absorption spectroscopy technique. A nonvariational RRKM calculation using previously determined thermodynamic parameters for these two reactions was performed, providing a complete and coherent picture of the kinetics and equilibria for these reactions. In addition, the data were fitted to a simplified and commonly used form of an expression developed by Troe to extrapolate falloff data to obtain high- and low-pressure limiting rate constants. Parameters are provided that allow the calculation of the rate constants of the title reactions as a function of temperature and pressure. The data are well represented by the following limiting rate-constant expressions: reaction 1, k(o)(T) = (1.26 +/- 0.03) X 10(-30)(T/300)-4.0 +/- 0.2 cm6 molecule-2 s-1, k(oo)(T) = (2.8 +/- 0.2) X 10(-12)(T/300)-1.4 +/- 0.3 cm3 Molecule-1 s-1; reaction 2, k(o)(T) = (1.88 +/- 0.05) X 10(-30)(T/300)-3.2 +/- 0.2 cm6 molecule-2 s -1, k(oo)(T) = (2.9 +/- 0.2) X 10(-12)(T/300)-1.2 +/- 0.4 cm3 molecule-1 s-1.