AbstractEarlier work on the reactions of O(3P) atoms with HCl and HBr has been extended by measuring rate constants forA flow‐tube method was used with chemiluminescent monitoring of the removal of atomic oxygen. Rate constants were measured at temperatures between 340 and 489 K for (2a) and 295 and 419 K for (2b); they can be matched by the Arrhenius expressions:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{2a} = 3.7(\pm 0.9) \times 10^{- 12} \exp \left({\frac{{- (7.0 \pm 0.5kcal/mole)}}{{RT}}} \right) $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{2b} = 5.8(\pm 0.5) \times 10^{- 12} \exp \left({\frac{{- (3.5 \pm 0.2kcal/mole)}}{{RT}}} \right) $$\end{document}where the units are cm3molecule−1sec−1and the errors correspond to a single standard deviation. The results of a quasiclassical trajectory study of collisions of O(3P) with HCl (v= 0,1, and 2) and DCl (v= 0,1, and 2) are also reported. These strengthen the conclusion that, although the rates of reactions (1a) and (2a) are selectively enhanced by vibrationally exciting HCl or DCl, molecules with 0