Lindqvist-Reis, Patric
- Forschungszentrum Karlsruhe
Abstract
Time-resolved laser fluorescence spectroscopy (TRLFS) is used to study the hydration of the Cm3+ ion in acidified (0.1 M perchloric acid) H2O and D2O from 20 to 200degreesC. Strong temperature dependency is found for several of the spectroscopic quantities associated with the D-6'(7/2) --> S-8'(7/2) photoemission spectra, with similar relative changes in both solvents. The emission band shifts to lower energy with increasing temperature, which is attributed to an equilibrium between hydrated Cm3+ ions with different numbers of water molecules in the first coordination sphere, namely [Cm(H2O)(9)](3+) and [Cm(H2O)(8)](3+). Comparison with crystalline reference compounds and the analysis of hot bands corroborates the assignment of these species. The molar fraction of the octahydrated species increases from similar to10% at room temperature to similar to40% at 200degreesC, indicating an entropy driven reaction. The corresponding thermodynamic parameters are obtained as DeltaHdegrees = + 13.1 +/- 0.4 kJ mol(-1), DeltaSdegrees = + 25.4 +/- 1.2 J mol(-1) K-1, and DeltaG(298) = + 5.5 +/- 0.6 U mol(-1) Both the emission intensity and lifetime decrease with increasing temperature. The temperature dependency of the nonradiative decay rate of the emitting 6D'7/2 level follows an Arrhenius equation with the activation energy 26.5 U mol(-1) (2250 cm(-1)) in both H2O and D2O, which is somewhat lower than the energy gap between D-6'(7/2) and P-6'(5/2) exited state levels.
Published in
Journal of Physical Chemistry B
2005, volume: 109, number: 7, pages: 3077-3083
Publisher: AMER CHEMICAL SOC
SLU Authors
UKÄ Subject classification
Inorganic Chemistry
Publication identifier
- DOI: https://doi.org/10.1021/jp045516+
Permanent link to this page (URI)
https://res.slu.se/id/publ/95540