2,4,6-trimethylbenzoyldiphenylphosphineoxide (TMDPO) was irradiated in dilute solutions of benzene, methanol and dichloromethane with 20 ns flashes of 347 nm light. By optical absorption measurements, a transient spectrum with a maximum at about 330 nm detected at the end of the flash was ascribed to the diphenyl phosphonyl radical . This radical is formed by the reaction. Evidence was obtained for fragment radicals being formed, to some extent at least, from triplet states. Both the singlet and the triplet lifetimes were estimated as τ < 1 ns.
