Reactions in aqueous solution containing ferrous sulfate are among the best understood of radiolytic reaction mechanisms, but hitherto unsuspected reactions must be taking place when large radiation doses are applied instantaneously in the presence of added chloride. We have recently found indications that yields under these conditions might be explicable if HO/sub 2/ radicals reduce Cl/sub 2/. This communication reports independent confirmation of this reaction, obtained in a system designed to demonstrate it. Microsecond pulses of fast electrons were delivered to oxygen-saturated solutions containing NaCl and HClO/sub 4/. Known reactions of the primary species OH, H, H/sub 2/, and H/sub 2/O/sub 2/, taken to be produced under our conditions with G = 3.1, 3.75, 0.4, and 0.7, respectively, are given in Table I (1 to 17). The concentration of HO/sub 2/ was calculated from optical absorption measurements made at 260 nm and allowing for a contribution at that wavelength from Cl/sub 2//sup -/. We conclude that HO/sub 2/ reduces Cl/sub 2/ with k = 1.0 x 10/sup 9/ M/sup -1/ s/sup -1/, i.e., close to the diffusion-controlled limit. The reaction may take place in various circumstances and should, for example, be considered together with some of the other reactions inmore » Table I when formulating free-radical mechanisms for the reaction between H/sub 2/O/sub 2/ and Cl/sub 2/.« less