The UV Absorption Spectrum of the CCl3 Radical and the Kinetics of Its Mutual Combination Reaction from 253 to 623 K.

The UV absorption spectrum and the kinetics of the self combination reaction of the CCl3 radical were studied by flash photolysis in the temperature range 253–623 K. Experiments were performed at the atmospheric pressure, except for a few runs at the highest temperatures, which were performed between 30 and 760 torr. CCl3 radicals were generated by flash photolysis of molecular chlorine in the presence of chloroform. The UV spectrum exhibits a strong unstructured band between 195 and 260 nm with a maximum at 211 ± 2 nm. The absorption cross section, measured relative to σ(HO2), is σ(CCl3) = (1.45 ± 0.35) × 10−17 cm2 molecule−1 at the maximum. This value takes into account the uncertainty in σ(HO2) which was taken equal to (4.9 ± 0.7) × 10−18 cm2 molecule−1. The absolute rate constant for the CCl3 mutual combination was determined by computer simulation of the transient decays. The rate constant, which exhibits a slight negative temperature coefficient, can be expressed as: The study of the pressure dependence showed that only a slight fall-off behavior could be observed at the highest temperature (623 K). This result was corroborated by RRKM calculations which showed that the rate constant is at the high pressure limit under most experimental conditions below 600 K.