PHOTOCHEMISTRY OF THE URANYL-ION WITH ALKENES IN ACETONE WATER MIXTURES

Quenching reactions of the excited uranyl ion with various alkenes (1-heptene, 1-hexene, 1-octene, cycloheptene, cyclohexene, 1,4-cyclohexadiene, 2,4-hexadiene and 1,3-cyclohexadiene) were studied in aqueous 50% acetone mixtures. The quenching constants k(q) Of various alkenes were determined by measuring the emission intensity and by the laser flash photolysis method. A plot of log k(q) vs. the free-enthalpy change DELTA-G2 for the photo-induced electron transfer showed a linear relationship, but the slope (1.0 eV-1) was much smaller than that predicted from the Rehm-Weller correlation. This indicates that direct electron transfer from alkene to excited uranyl ion was not the rate-determining step. These quenching reactions resulted in the formation of uranium(IV), except for the reactions with alkenes of high vertical ionization potentials. The quantum yields for the formation of uranium(IV) were measured. A plot of the reciprocal quantum yield for the reaction with 1,4-cyclohexadiene vs. its reciprocal concentration gave a straight line.