Isothermal gas chromatography study of Zr and Hf tetrachlorides using radiotracers of ⁸⁸Zr and ¹⁷⁵Hf

—Towards investigation of gas-phase chemistry of Rf—

Abstract

Experiments on gas-phase chemistry for chlorides have been conducted to clarify chemical properties of the first superheavy element, rutherfordium (Rf), Z = 104. However, adsorption enthalpies obtained in each experiment are not the same, even for those of the homologues Zr and Hf. In the present study, off-line isothermal gas chromatography was done using long-lived radioactive tracers to obtain reliable adsorption enthalpies for ZrCl₄ and HfCl₄ when adsorbed on a quartz glass surface. To simulate a column surface modified by a chlorinating reagent in on-line experiments, chromatography was also performed using a chlorinated column. A newly developed analytical method which is independent of experimental parameters and uncertain physical quantities was applied to determine the adsorption enthalpies. The obtained enthalpies for ZrCl₄ and HfCl₄ were -101.3 ± 4.0 kJ mol^-1 and -98.1 ± 3.1 kJ mol^-1 for the non-treated column, respectively, and those for the chlorinated column were -85.1 ± 4.5 kJ mol^-1 and -84.2 ± 3.3 kJ mol^-1, respectively.