Abstract: A rotating disk reactor for producing singlet delta oxygen is disclosed. The reactor includes a plurality of closely spaced coaxial disks partially immersed in a pool of liquid basic hydrogen peroxide (BHP) inside a reactor vessel. A thin film of BHP is picked up and carried on the rotating disks. Chlorine gas, diluted with helium, is flowed into the reactor vessel to pass between the disks and react with the BHP to produce singlet delta oxygen. The singlet delta oxygen flows out of the reactor through a liquid separator to remove liquids and then through an impurity cold trap to remove by condensation gaseous H.sub.2 O.sub.2 and H.sub.2 O.