TRLFS study on the complexation of Cm(III) with nitrate in the temperature range from 5 to 200 °C

The formation of aqueous Cm(III) nitrate complexes is studied in the temperature range from 5 to 200 °C by time resolved laser fluorescence spectroscopy (TRLFS). The experiments are performed in a custom build high pressure and high temperature fluorescence cell. The complex formation is measured at nitrate concentrations ranging from 0.10 to 4.61 mol/kg H 2 O. The mono- and dinitrate complexes are quantified by peak deconvolution of the fluorescence spectra and the complexation constants are determined as a function of the temperature. The conditional equilibrium constants are extrapolated to zero ionic strength using the specific ion interaction theory (SIT) and the thermodynamic standard state data (Δ r H ° m , Δ r S ° m , Δ r G ° m , Δ r C ° p,m ) are determined from the temperature dependence of the equilibrium constants at I =0. The equilibrium constants up to 75 °C are well described by the Van´t Hoff equation (Δ r H ° m independent of T and Δ r C ° p,m =0). Modelling of the data at higher temperatures requires an extended equation including a term for the heat capacity changes (Δ r C ° p,m ).