The potential energy surfaces of the reactions 0 atoms with HOX (X = Cl, Br) are investigated by MPW1K, QCISD, G3(MP2) (single-point) levels. There are two abstraction channels, i.e., hydrogen and halogen (Cl and Br) abstraction channels to form the same products OH + XO (X = Cl and Br). The present theoretical results bring forward different reaction mechanism for HOCl + O, which was presented in the period study. The rate constants are carried out by the improved canonical variational transition state theory (ICVT) over a wide temperature range 200-2000 K. Agreement between the ICVT rate constants and the experimental values is good. Our calculations show that the halogen abstraction channel predominates the reaction over the whole temperature range for both reactions and the rate constants increase with the temperature increasing. (c) 2005 Elsevier B.V. All rights reserved.