Quantum yield and electron-transfer reaction of the lowest excited state of uranyl ion

T. Rosenfeld-Grünwald, J. Rabani*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

The pulsed photoreduction (using N2 laser photolysis technique) of uranyl ion, UO22+, both in its ground state and in the lowest excited state (at pH 2 and in 2 M H3PO4 aqueous solutions) has been studied. We found that *UO22+ is quenched by ruthenium tris(bipyridine) ions, Ru(bpy)32+, and Ru(bpy)33+ is formed; namely, *UO22+ is an electron-acceptor species. It is shown here that the rate of decay of *UO22+ in the presence of Ru(bpy)32+ exactly corresponds to the formation rate of Ru(bpy)33+, as measured by the bleaching of the Ru(bpy)32+ ground-state absorption. The excited state of Ru(bpy)32+ is found to be quenched by UO22+, and again Ru(bpy)33+ is formed, UO22+ being an electron acceptor in its ground state. The quantum yield of the formation of the lowest excited state of UO22+, φ*UO22+, multiplied by the yield of electron transfer, φetRu→*U, between *UO22+ and Ru(bpy)32+ is found to be 0.5 at pH 2 and unity in 2 M H3PO4 solution. In the presence of a negatively charged polyelectrolyte, such as poly(vinyl sulfate), PVS, the value of this product is reduced to an upper limit of 0.1. It is shown that φ*UO22+ is unaffected by the presence of PVS. The back reaction, UO2+ + Ru(bpy)33+ → UO22+ + Ru(bpy)32+, is a second-order reaction, k/ε (λ = 450 nm) = 1.05 × 105 s-1 cm at pH 2 and 1.78 × 102 s-1 cm in 2 M H3PO4 solution. This reaction is accelerated in the presence of O2 or PVS. The yields and rates of formations and reactions of the photochemical products are discussed.

Original languageEnglish
Pages (from-to)2981-2985
Number of pages5
JournalJournal of Physical Chemistry
Volume84
Issue number22
DOIs
StatePublished - 1980

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