VLPR study of the reaction Br + CH 3 CHO

The reaction \documentclass{article}\pagestyle{empty}\begin{document}${\rm Br} + {\rm CH}_3 {\rm CHO}\buildrel1\over\rightarrow{\rm HBr} + {\rm CH}_3 {\rm CO}$\end{document} has been studied by VLPR at 300 K. We find k 1 = 2.1 × 10 12 cm 3 /mol s in excellent agreement with independent measurements from photolysis studies. Combining this value with known thermodynamic data gives k ‐1 = 1 × 10 10 cm 3 /mol s. Observations of mass 42 expected from ketene suggest a rapid secondary reaction:\documentclass{article}\pagestyle{empty}\begin{document}$${\rm Br} + {\rm CH}_3 {\rm CO}\buildrel2\over\rightarrow[{\rm CH}_3 {\rm COBr}]^* \buildrel3\over\rightarrow{\rm HBr} + {\rm CH}_2 {\rm CO}$$\end{document}in which step 2 is shown to be rate limiting under VLPR conditions and k 2 is estimated at 10 12.6 cm 3 /mol s from recent theoretical models for radical recombination. It is also shown that 0 ⩽ E 1 ⩽ 1.4 kcal/mol using theoretical models for calculation of A 1 and is probably closer to the lower limit. Reaction −1 is negligible under conditions used.