A computational study of the reaction kinetics of methyl radicals with trifluorohalomethanes

✍ Scribed by R. J. Berry; Paul Marshall

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 153 KB
• Volume: 30
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1998)30:3<179::aid-kin2>3.0.co;2-p

✦ Synopsis

Ab initio calculations have been used to characterize the transition states for halogen abstraction by CH 3 in reactions with CF 4 , CF 3 Cl, CF 3 Br, and CF 3 I (1-4). Geometries and frequencies were obtained at the HF/6-31G(d) and levels of theory. En-MP2 ϭ full/6-31G(d) ergy barriers were computed via the Gaussian-2 methodology, and the results were employed in transition state theory analyses to obtain the rate constants over There is 298-2500 K. good accord with literature measurements in the approximate temperature range 360-500 K for reactions (2-4), and the computed activation energies are accurate to within Ϯ Recommended rate constant expressions for use in combustion modeling Ϫ1 6 kJ mol . are Ϫ19 2.41 Ϫ20 2.34 k ϭ 1.6 ϫ 10 (T/K) exp(Ϫ13150 K/T), k ϭ 8.4 ϫ 10 (T/K) exp(Ϫ5000 K/T), 1 2 and Ϫ19 2.05 Ϫ19 2.18 3 k ϭ 4.6 ϫ 10 (T/K) exp(Ϫ3990 K/T), k ϭ 8.3 ϫ 10 (T/K) exp(Ϫ1870 K/T) cm 3 4 molecul The results are discussed in the context of flame suppression chemistry.