Journal of Physical Chemistry A, Vol.114, No.14, 4805-4810, 2010
Kinetics of the Reactions of CH2Cl, CH3CHCl, and CH3CCl2 Radicals with Cl-2 in the Temperature Range 191-363 K
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 CH3CHCl + Cl-2 reaction obtained from the current measurements exhibit negative temperature dependence and can be expressed by the equation k(CH3CHCl + Cl-2) = ((3.02 +/- 0.14) x 10(-12))(T/300 K)(-1.8 +/- 0.19) cm(3) molecule(-1) s(-1) (1.7-5.4 Torr, 191-363 K). For the CH3CCl2 + Cl-2 reaction the current results could be fitted with the equation k(CH3CCl2 + Cl-2) = ((1.23 +/- 0.02) x 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,CI + CI, 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(CH2Cl + Cl-2) = ((2.11 +/- 1.29) x 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 CH3CCl2 + Cl-2 and CH2Cl + CI, reactions can be combined with previous results to obtain: k(combined)(CH3CCl2 + Cl-2 ) = ((4.72 +/- 1.66) x 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(comhined)(CH2Cl + Cl-2) = ((5.18 +/- 1.06) x 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 la statistical uncertainties obtained from the fitting, and the estimated overall uncertainty in the determined bimolecular rate coefficients is about +/- 15%.