Abstract: A process for generating an excited molecular oxygen by a procedure which comprises causing a mixture of an alkaline aqueous solution with hydrogen peroxide to wet the surface portion of a layer of a hydrophilic and gas-pervious material, causing a molecular chlorine-containing gas to penetrate said layer from the side opposite said surface thereof, enabling said gas during the penetration thereof through said material to react with said mixed aqueous solution which has wetted said surface portion of said material, and thereby inducing generation of said excited molecular oxygen, O.sub.2 (.sup.1 .DELTA.), through said surface portion of said layer wetted by said mixed aqueous solution.