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

Abstract

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 248 Cm( 18 O, 5n) reaction. 165-167 Hf was produced via the reaction nat Eu( 19 F, xn), and 85 Zr was produced via the nat Cu( 28 Si, 3p3n) reaction. The half-life for 261 Rf was measured to be 75±7 seconds. A Monte Carlo code was used to deduce the enthalpy of adsorption (ΔH 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 -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.