Title: Complexation of Cm(III) with Fluoride in Aqueous Solution in the Temperature Range from 20 to 90 °C. A joint TRLFS and Quantum Chemical Study
Citation: JOURNAL OF PHYSICAL CHEMISTRY vol. 114 p. 15626-15634
Publication Year: 2010
JRC N°: JRC58251
ISSN: 0022-3654
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC58251
DOI: 10.1021/jp107794u
Type: Articles in periodicals and books
Abstract: The formation of hydrated CmF2+ and CmF2+ species in aqueous solutions are studied in the temperature range of 20 to 90 °C at different fluoride concentrations and at constant ionic strength as well as at constant fluoride concentration and different ionic strengths by means of Time Resolved Laser Fluorescence Spectroscopy (TRLFS). The molar fractions of the Cm3+ aquo ion, CmF2+ and CmF2+ species are determined by peak deconvolution of the emission spectra. An increase of the mono- and difluoro complexes is observed with increasing fluoride concentration and/or increasing temperature. Using the specific ion interaction theory (SIT), the thermodynamic stability constants log K01 (CmF2+) and log K02 (CmF2+) as well as the values of ¿e1 and ¿e2 are determined as function of temperature. The log K01 values increase from 3.56 ± 0.07 to 3.98 ± 0.06 and the log K02 values increase from 2.20 ± 0.84 to 3.34 ± 0.21 with increasing temperature from 20 to 90 °C. The value of ¿e1 determined at T = 25°C is in good agreement with literature data and shows a negligible temperature dependency in the studied temperature range. The value of ¿e2 also shows only a moderate variation in the studied temperature range. The thermodynamic standard state data (¿rH0m, ¿rS0m, ¿rG0m) are determined from the temperature dependence of the equilibrium constants at Im = 0 using the integrated Van¿t Hoff equation. The fluorescence lifetime of the 6D¿7/2(Cm3+) state is found to be constant at 63 ± 5 µs with increasing fluoride concentration. A model based on DFT calculations is introduced to account for the additional fluorescence quenching occurring through the near second sphere waters in the [Cm(H2O)8F]2+(H2O)18 complex.
JRC Directorate:Nuclear Safety and Security

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