✍ Scribed by Yoon-Yul Park; Hiroshi Tomiyasu
No coin nor oath required. For personal study only.
Quenching reactions of the excited uranyl ion with various alkenes (1-heptene, 1-hexene, I-octene, cycloheptene, cyclohexene, 1,4_cyclohexadiene, 2,4-hexadiene and 1,3-cyclohexadiene) were studied in aqueous 50% acetone mixtures. The quenching constants kg of various alkenes were determined by measuring the emission intensity and by the laser flash photolysis method. A plot of log kg vs. the free-enthalpy change AG, for the photoinduced electron transfer showed a linear relationship, but the slope (1.0 eV_') 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.
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