A mechanism for the production of singlet oxygen by acidification of hypochlorite in aqueous solution is proposed based on electron structure calculations. The mechanism involves two transition states and a peroxyhypochlorous acid intermediate. The calculations include six explicit water molecules to give some allowance for solvation of the produced electrolyte. The theoretical level is the density functional theory and the isodensity polarized continuum method. (c) 2007 Elsevier B.V. All rights reserved.