A spectroscopic study on the formation of Cm(iii) acetate complexes at elevated temperatures

Abstract

The complexation of Cm(III) with acetate is studied by time resolved laser fluorescence spectroscopy (TRLFS) as a function of ionic strength, ligand concentration, temperature and background electrolyte (NaClO₄, NaCl and CaCl₂ solution). The speciation of Cm(III) is determined by peak deconvolution of the emission spectra. To obtain the thermodynamic stability constants (log K⁰_n) for the formation of [Cm(Ac)_n]³⁻ⁿ (n = 1–3), the experimental data are extrapolated to zero ionic strength according to the specific ion interaction theory (SIT). The results show a continuous increase of the stability constants with increasing temperature (20–90 °C). The standard reaction enthalpies and entropies (Δ_rH⁰_m, Δ_rS⁰_m) of the respective reactions are derived from the integrated Van't Hoff equation. The results show that all complexation steps are endothermic and thus entropy driven (Δ_rH⁰_m and Δ_rS⁰_m > 0).