No abstract

The periodic table provides a classification of the chemical properties of the elements. But for the heaviest elements, the transactinides, this role of the periodic table reaches its limits because increasingly strong relativistic effects on the valence electron shells can induce deviations from known trends in chemical properties. In the case of the first two transactinides, elements 104 and 105, relativistic effects do indeed influence their chemical properties, whereas elements 106 and 107 both behave as expected from their position within the periodic table. Here we report the chemical separation and characterization of only seven detected atoms of element 108 (hassium, Hs), which were generated as isotopes (269)Hs (refs 8, 9) and (270)Hs (ref. 10) in the fusion reaction between (26)Mg and (248)Cm. The hassium atoms are immediately oxidized to a highly volatile oxide, presumably HsO(4), for which we determine an enthalpy of adsorption on our detector surface that is comparable to the adsorption enthalpy determined under identical conditions for the osmium oxide OsO(4). These results provide evidence that the chemical properties of hassium and its lighter homologue osmium are similar, thus confirming that hassium exhibits properties as expected from its position in group 8 of the periodic table.

In preparation for the experimental investigation of chemical properties of element 112 model studies were conducted based on the assumed similarity of element 112 to either the noble gas Rn or the transition metal Hg, its supposed lighter homologue in group 12. The adsorption behavior of elemental Hg on the transition metals Ag, Au, Ni, Pd, and Pt were investigated experimentally by off-line gas thermochromatography. The deduced adsorption data of Hg were compared with new values calculated using the Eichler-Miedema model. The observed sequence of increasing Hg-metal-interactions for Ag < Ni < Au < Pd < Pt confirms the predicted trend. The only exception was Pd, on which Hg was calculated to adsorb at a higher temperature than on Pt. Difficulties to obtain reproducible clean surfaces of Ag, Ni, Pd, and Pt led to the choice of Au as the best metal surface suitable to adsorb Hg.For fast on-line gas thermochromatography studies on metallic surfaces a new set-up was developed based on the In-situ Volatilization and On-line detection technique (IVO). This set-up was tested in on-line thermochromatographic investigations with short-lived Hg isotopes and 219 Rn, using Au or Pd as stationary surfaces. An overall efficiency of about 60% and a transportation time less than 25 s was determined for this newly designed IVO. A separation factor of more than 10 6 was estimated for non-volatile species.

Recently efficient blue-white luminescence from Sr 2 CeO 4 was reported. 1 The emission was assigned to a ligand-to-metal chargetransfer transition of Ce 4ϩ . Charge transfer (CT) emission from Ce 4ϩ , or any other tetravalent lanthanide, had not been reported previously. Here, further research on the luminescence of Sr 2 CeO 4 is reported. Three topics are discussed. First the nature of the luminescence is investigated. The results provide evidence that the efficient blue-white emission is not related to a lattice defect and support the assignment of the emission to a Ce 4ϩ -O 2Ϫ CT transition. Second, lifetime measurements are discussed. The lifetime, 65 Ϯ 5 s at 6 K, is long for a parity allowed CT transition. The spin-forbidden nature of the emission can explain the observed lifetime. Finally, the temperature dependence of the emission intensity and luminescence lifetime is investigated. At 300 K both the emission intensity and the lifetime are reduced to about 50% of the values at 6 K. This shows that the quantum efficiency measured to be about 40% at room temperature is close to the maximum efficiency at room temperature. The low quenching temperature is a serious drawback for application of Sr 2 CeO 4 as a phosphor in lighting.