Spectroscopic Properties and Hydration of the Cm(III) Aqua Ion from 10 to 85 °C

The optical absorption, fluorescence excitation, and emission spectra of the Cm(III) aqua ion in 0.001 M perchloric acid were studied in pure H2O, pure D2O, and in mixtures of H2O D2O at temperatures from 10 to 85 degrees C. The quantum yield of the fluorescence of the Cm(III) aqua ion in pure H2O and D2O was also measured in this temperature range and the radiative decay rate constant was obtained from these data. The results indicate that, from 10 to 85 degrees C, the effect of temperature on the absorption, excitation, and emission spectra is very small. By correcting the observed decay rate constant for the radiative rate constant, a set of correlations between the observed fluorescence decay rate constant and the hydration number of Cm3+ in H2O at temperatures from 10 to 85 degrees C was developed. A weak temperature dependence was observed for the nonradiative decay rate constant for the D-6(7/2)'-S-8(7/2)' transition and described by the Arrhenius equation. The activation energy of the nonradiative decay was measured to be 0.9 kJ mol(-1), approximately matching the energy gap between the first and the second (A(1) and A(2)) levels of the metastable D-6(7/2)' multiplet of the Cm(III) aqua ion. On the basis of these observations, it is postulated that the slight increase in the observed fluorescence decay rate constant as the temperature increases from 10 to 85 degrees C is due to the effect of thermal population of the A(2) level.