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-cyclohexad iene, 2,4-hexadiene and 1,3-cyclohexadiene) were studied in aqueous 50 % acetone mixtures. The quenching constants k(q) Of various alkenes we re determined by measuring the emission intensity and by the laser fla sh photolysis method. A plot of log k(q) vs. the free-enthalpy change DELTA-G2 for the photo-induced electron transfer showed a linear relat ionship, 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-determini ng step. These quenching reactions resulted in the formation of uraniu m(IV), except for the reactions with alkenes of high vertical ionizati on potentials. The quantum yields for the formation of uranium(IV) wer e measured. A plot of the reciprocal quantum yield for the reaction wi th 1,4-cyclohexadiene vs. its reciprocal concentration gave a straight line.