The potential energy surface for the reactions CH3 + OClO (1), CH3O + ClO (2) and CH3O2 + Cl (3) is investigated using ab initio quantum mechanical methods. The calculations indicate the intermediate formation of two important isomeric energy minima, CH3OCIO and CH3OOCI. H2CO + HOCl and CH3O + ClO are shown to be the most probable products for reaction (1) and H2CO + HOCl and CH2O2 + HCl for reaction (2). Reaction (3) most probably leads to either CH2O2 + HCl or CH3O + ClO. (C) 2003 Elsevier Science B.V. All rights reserved.