Here we show that the photolysis of FeCl2+ upon UV irradiation of Fe(III) at pH 0.5, yielding Cl� and then Cl2-�, upon further reaction with Cl-, induces phenol degradation. The photolysis of FeCl2+ can be highlighted and studied as the huge interference by FeOH2+ can be avoided under such conditions. Our data allowed the assessment of a photolysis quantum yield for FeCl2+ of 5.8 � 10-4 under UVA irradiation, much lower compared to the literature value of 0.5. The discrepancy can be explained if the photolysis process is efficient but photoformed Fe2+ and Cl� undergo recombination inside the solvent cage. © Springer-Verlag 2007.