Laser Photolysis Studies of the Reduction of Paraquat Cations in Methanol

A computer‐controlled laser photolysis apparatus has been used to investigate the results of photoexcitation of paraquat. cations (PQ2+) in methanol solution. The formation of the monoreduced species (PQ+) is shown to occur in two processes overall; one is too fast to be resolved from the laser pulse; the second shows first order kinetics with an observed rate constant which is linearly dependent on the paraquat concentration. The natural lifetime of this second precursor to PQ+ was measured at 1.4 μs. about ten times longer than the CH3O'radical which is the anticipated reductant. The identity of this precursor is possibly a radical pair.