Kinetics of the Reactions of CH₂Cl, CH₃CHCl, and CH₃CCl₂ Radicals with Cl₂ in the Temperature Range 191−363 K (original) (raw)

The kinetics of three chlorinated free radical reactions with Cl 2 have been studied in direct time-resolved measurements. Radicals were produced in low initial concentrations by pulsed laser photolysis at 193 nm, and the subsequent decays of the radical concentrations were measured under pseudo-first-order conditions using photoionization mass spectrometer (PIMS). The bimolecular rate coefficients of the CH 3 CHCl + Cl 2 reaction obtained from the current measurements exhibit negative temperature dependence and can be expressed by the equation k(CH 3 CHCl + Cl 2)) ((3.02 (0.14) × 10-12)(T/300 K)-1.89(0.19 cm 3 molecule-1 s-1 (1.7-5.4 Torr, 191-363 K). For the CH 3 CCl 2 + Cl 2 reaction the current results could be fitted with the equation k(CH 3 CCl 2 + Cl 2)) ((1.23 (0.02) × 10-13)(T/300 K)-0.26(0.10 cm 3 molecule-1 s-1 (3.9-5.1 Torr, 240-363 K). The measured rate coefficients for the CH 2 Cl + Cl 2 reaction plotted as a function of temperature show a minimum at about T) 240 K: first decreasing with increasing temperature and then, above the limit, increasing with temperature. The determined reaction rate coefficients can be expressed as k(CH 2 Cl + Cl 2)) ((2.11 (1.29) × 10-14) exp(773 (183 K/T)(T/300 K) 3.26(0.67 cm 3 molecule-1 s-1 (4.0-5.6 Torr, 201-363 K). The rate coefficients for the CH 3 CCl 2 + Cl 2 and CH 2 Cl + Cl 2 reactions can be combined with previous results to obtain: k combined (CH 3 CCl 2 + Cl 2)) ((4.72 (1.66) × 10-15) exp(971 (106 K/T)(T/300 K) 3.07(0.23 cm 3 molecule-1 s-1 (3.1-7.4 Torr, 240-873 K) and k combined (CH 2 Cl + Cl 2)) ((5.18 (1.06) × 10-14) exp(525 (63 K/T)(T/300 K) 2.52(0.13 cm 3 molecule-1 s-1 (1.8-5.6 Torr, 201-873 K). All the uncertainties given refer only to the 1σ statistical uncertainties obtained from the fitting, and the estimated overall uncertainty in the determined bimolecular rate coefficients is about (15%.