Temperature dependence of the rate coefficients for the reaction of chlorine atoms with chloromethanes

✍ Scribed by John J. Orlando

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 192 KB
• Volume: 31
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1999)31:7<515::aid-kin6>3.0.co;2-1

✦ Synopsis

Rate coefficients for the reaction of Cl atoms with CH 3 Cl (k 1 ), CH 2 Cl 2 (k 2 ), and CHCl 3 (k 3 ) have been determined over the temperature range 222-298 K using standard relative rate techniques. These data, when combined with evaluated data from previous studies, lead to the following Arrhenius expressions (all in units of cm 3 molecule Ϫ1 s Ϫ1 ):

Values for k 1 are in substantial agreement with previous measurements. However, while the room temperature values for k 2 and k 3 agree with most previous data, the activation energies for these rate coefficients are substantially lower than previously recommended values.

In addition, the mechanism of the oxidation of CH 2 Cl 2 has been studied. The dominant fate of the CHCl 2 O radical is decomposition via Cl-atom elimination, even at the lowest temperatures studied in this work (218 K). However, a small fraction of the CHCl 2 O radicals are shown to react with O 2 at low temperatures. Using an estimated value for the rate coefficient of the reaction of CHCl 2 O with O 2 (1 ϫ 10 Ϫ14 cm 3 molecule Ϫ1 s Ϫ1 ), the decomposition rate coefficient for CHCl 2 O is found to be about 4 ϫ 10 6 s Ϫ1 at 218 K, with the barrier to its decomposition estimated at 6 kcal/mole. As part of this work, the rate coefficient for Cl atoms with HCOCl was also been determined, k 7 ϭ 1.4 ϫ 10 Ϫ11 exp(Ϫ885/T) cm 3 molecule Ϫ1 s Ϫ1 , in agreement with previous determinations.