Unimolecular reaction dynamics of CH3COCl and FCH2COCl : An infrared chemiluminescence and ab initio study

Srivatsava, A. ; Arunan, E. ; Manke II, G. ; Setser, D. W. ; Sumathi, R. (1998) Unimolecular reaction dynamics of CH3COCl and FCH2COCl : An infrared chemiluminescence and ab initio study Journal of Physical Chemistry A, 102 (32). pp. 6412-6420. ISSN 1089-5639

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Official URL: http://pubs.acs.org/doi/abs/10.1021/jp980415v

Related URL: http://dx.doi.org/10.1021/jp980415v


The F+CH3COCl and H+ICH2COCl reaction systems were studied by the infrared chemiluminescence method in a flow reactor. The primary reaction of F+CH3COCl gives a nascent HF(v) distribution of P1-P3 =21:52:27. A linear surprisal analysis gives P0=3 and ƒv(HF) = 0.60, which is typical for H abstraction reactions by F atoms. The C-H bond energy in acetyl chloride is estimated as ≤101.2 kcal mol−1, from the highest HF(v, J) level populated in the primary reaction. The H + ICH2COCl primary reaction leads to HI + CH2COCl. The secondary F+CH2COCl and H + CH2COCl reactions give chemically activated FCH2COCl/CH3COCl molecules. The 1,2-HCl elimination channel is the dominant unimolecular pathway for both reactions under our experimental conditions. The HCl(v) distribution from CH3COCl is P1-P4=39:32:20:9. Surprisal analysis was used to estimate the P0 value as 36% and <ƒv(HCl)>=0.12. The reaction time had to be increased from ≤0.2 ms to ≥0.5 ms to record the HCl(v) emission from F + CH2COCl, and the best distribution was P1-P4+ 68:24:5:3. The estimated ?ƒv(HCl)? was only 0.06 which is a lower limit due to HCl(v) relaxation. The CO(v =1 → 0) emission could also be observed from this reaction with an intensity that was typically less than 10% of the HCl(v) emission. Ab initio calculations for FCH2COCl at MP2/6-31G* level give the threshold energy for HCl elimination as 61 kcal mol−1, which is 12 kcal mol−1 larger than that for CH3COCl at the same level. The threshold energies for the other reactions of FCH2COCl are 81.0 for CO elimination, 82.5 for C-C dissociation, and 78.4 for C-Cl dissociation. RRKM and ab initio calculations indicate that CO formation results from the FCH2COCl → FCH2+COCl dissociation step followed by COCl → CO+ Cl. For CH3COCl*, with 105 kcal mol−1 energy, HCl elimination accounts for 98% of the total reaction and C-C dissociation accounts for the rest. The C-Cl dissociation channel is not important for either molecule at these energies.

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