Kinetics and mechanism of the reaction of Cl atoms with CH2 CO (Ketene)

✍ Scribed by T. J. Wallington; J. C. Ball; A. M. Straccia; M. D. Hurley; E. W. Kaiser; M. Dill; W. F. Schneider; M. Bilde

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 553 KB
• Volume: 28
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/(sici)1097-4601(1996)28:8<627::aid-kin8>3.0.co;2-x

✦ Synopsis

The kinetics and mechanism of the gas-phase reaction of CI atoms with CH,CO have been studied with a fTIR spectrometer/smog chamber apparatus. Using relative rate methods the rate of reaction of CI atoms with ketene was found to be independent of total pressure over the range 1-700 torr of air diluent with a rate constant of ( 2 7 ? 0.5) X lo-" cm3 molecule-' s ~ ' at 295 K. The reaction proceeds via an addition mechanism to give a chloroacetyl radical (CH,CICO) which has a high degree of internal excitation and undergoes rapid unimolecular decomposition to give a CH,CI radical and CO. Chloroacetyl radicals were also produced by the reaction of CI atoms with CH,CICHO; no decomposition was observed in this case. The rates of addition reactions are usually pressure dependent with the rate increasing with pressure reflecting increased collisional stabilization of the adduct. The absence of such behavior in the reaction of CI atoms with CH,CO combined with the fact that the reaction rate is close to the gas kinetic limit is attributed to preferential decomposition of excited CH,CICO radicals to CH,CI radicals and CO as products as opposed to decomposition to reform the reactants As part of this work ab initio quantum mechanical calculations [MP2/6-31G[d.p)) were used to derive A fH,,,(CH2CICO) = -15.4 ? 4.0) kcal mol-' 0 1996 john Wiley & Sons, Inc