Coordination of trivalent actinides by humic acids: a TRLFS study

The fluorescence lifetime of humate complexed Cm(III) is studied in water and D2O media. The fluorescence decay function is a combination of the impact of the humic acid ligand backbone and quenching by hydration water in the coordination sphere of the complexed Cm(III) ion. The energy transfer between the complexed Cm(III) ion and the humic acid backbone results in a bi-exponential fluorescence decay function. The additional quench impact of water molecules in the inner coordination sphere of the complexed Cm(III) ion is evaluated by the difference in water and D2O medium. The outcome is that three water molecules are found in the inner coordination sphere, presumably with the residual six coordination sites occupied by functional groups of the humic acid. (orig.)