Formation of volatile curium(VI) trioxide CmO3
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Thermal oxidation of trace amounts of curium hydride yields a volatile form of CmO2 and the previously unknown trioxide CmO3. They were separated by gas thermochromatography. Under the experimental conditions, the maxima of the deposition zones of Cm oxides on the surface of the quartz column were at 550 ± 25 and 390 ± 25°C, respectively. The calculated enthalpies of adsorption on quartz (kJ mol−1) were 185 ± 25 (for CmO2) and 157 ± 25 (for CmO3). Lower volatility of Cm di- and trioxide, compared to the analogous oxides of U, Np, Pu, and Am, is attributed to a decrease in the ionic radii of actinides along the actinide series and to the break in the order of filling of the 5f shell in going from Am to Cm. The existence of volatile oxyfluoride and hexafluoride of Cm(VI) was suggested.