Thermodynamic analysis of volatile organometallic fission products
The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasi-closed electron shell configurations of 6d(10)7s(2) and 6d(10)7s(2)7p1/2(2), respectively, predicted them to be noble-gas-like due to very strong relativistic effects on the 7s and 7p1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologues in the groups, but still exhibiting a metallic character. Experimental gas-solid chromatography studies on Cn have, indeed, revealed a metal-metal bond formation with Au. In contrast to this, for Fl, the formation of a weak bond upon physisorption on a Au surface was inferred from first experiments. Here, we report on a gas-solid chromatography study of the adsorption of Fl on a Au surface. Fl was produced in the nuclear fusion reaction (244)Pu((48)Ca, 3-4n)(288,289)Fl and was isolated in-flight from the primary (48)Ca beam in a physical recoil separator. The adsorption behavior of Fl, its nuclear α-decay product Cn, their lighter homologues in groups 14 and 12, i.e., Pb and Hg, and the noble gas Rn were studied simultaneously by isothermal gas chromatography and thermochromatography. Two Fl atoms were detected. They adsorbed on a Au surface at room temperature in the first, isothermal part, but not as readily as Pb and Hg. The observed adsorption behavior of Fl points to a higher inertness compared to its nearest homologue in the group, Pb. However, the measured lower limit for the adsorption enthalpy of Fl on a Au surface points to the formation of a metal-metal bond of Fl with Au. Fl is the least reactive element in the group, but still a metal.