. Can. J. Chem. 52,3728(1974). Various transition metal chelates were found to quench '0, in the liquid phase. '0, was generated either photochemically, from an ozonide, or with a microwave source and reacted with rubrene or 3-methyl-2-pentene. Rate constants for '02 quenching by the chelates were measured in various solvents using the three '0, sources? and compared with the constants of previously known '02 quenchers. The most efficient chelates quenched '0, at close to the diffusion controlled rate, as did B-carotene. Some quenchers of '0, in the liquid phase were qualitatively shown to quench in the solid state. The possible '0, quenching mechanisms of the chelates are discussed.