On-line gas chromatographic studies of Rf, Zr, and Hf bromides

The Heavy Element Volatility Instrument (HEVI), an on-line isothermal gas chromatography system, has been used to separate the volatile bromide compounds of the group 4 elements Zr and Hf and the transactinide Rf according to their volatilities, and to provide data on the gas phase chemical properties of very short-lived isotopes in amounts as low as a few atoms. For these studies 261Rf was produced via the 248Cm(18O, 5n) reaction. 165-167Hf was produced via the reaction natEu(19F, xn), and 85Zr was produced via the natCu(28Si, 3p3n) reaction. The half-life for 261Rf was measured to be 75±7 seconds. A Monte Carlo code was used to deduce the enthalpy of adsorption (ΔHa) from the observed volatility and parameters of the chromatography system. The resulting adsorption enthalpies for the Zr, Hf, and Rf tetrabromides are: -108±5 kJ · mol-1, -113±5 kJ · mol-1 and -87±7 kJ · mol-1, respectively. Volatilities of the group 4 bromides support the conclusion from previous results for the group 4 chlorides that Rf deviates from the trend expected by simple extrapolation of the properties of its lighter homologs in the periodic table. The group 4 bromides are also observed to be less volatile than their respective chlorides, as predicted by relativistic calculations.