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 (261)Rf was produced via the Cm-248(O-18, 5n) reaction. Hf165-167 was produced via the reaction Eu-nat(F-19, xn), and Zr-85 was produced via the Cu-nat(Si-28, 3p3n) reaction. The hair-life for (261)Rf was measured to be 75 +/- 7 seconds. A Monte Carlo code was used to deduce the enthalpy of adsorption (DeltaH(a)) 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 -877 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.