The energetics for Cl2O2 isomers and their cations as well as the fragments of these species have been investigated at the Gaussian-2 level of ab initio theory. It is found that the calculated heats of formation and dissociation energies for Cl2O2 and Cl2O2+ isomers, as well as the ionization energies of the neutral species, are in good agreement with available experimental measurements. In addition, on the basis of these computational results, it may be concluded that both ClOOCl and ClOClO are formed in the dimerization of ClO.