The reactions of HOW with HCl and HBr in the presence of n = 0, 1, 2 and 3 water molecules are investigated by hybrid density functional theory methods in combination with canonical, variational transition state theory including tunneling corrections. Compared to the reactions of HOCl with HCl and HBr [J. Phys. Chem. A 106 (2002) 7850], we found that the barriers of the title reactions are significantly lower yielding much higher rate constants. Support of only two water molecules makes the reaction of HOW with HBr barrierless. Under stratospheric conditions the reactions of HOBr with HBr are the most reactive ones. (C) 2003 Elsevier Science B.V. All rights reserved.