ONLINE GAS-PHASE CHROMATOGRAPHY WITH CHLORIDES OF NIOBIUM AND HAHNIUM(ELEMENT-105)

The retention behavior of volatile chlorides and oxychlorides of short -lived isotopes of group 5 elements Nb and 105 (Ha = hahnium) in quart z columns was studied using on-line isothermal gas chromatography. The 15-s Nb-99g was produced from a U-235-fission target at a reactor neu tron beam line and 34-s (262)Ha in fusion reactions of O-18 + Bk-249. The reaction products were continuously and rapidly transported to the chromatography apparatus with a carbon aerosol gas-jet system using H e as carrier gas. Volatile chloride molecules were formed in a 900 deg rees C reaction oven by adding HCl as reactive gas. Depending on trace amounts of O-2 in the system, either the pentachlorides or the oxytri chlorides, or a mixture thereof, were formed. The isotopes Nb-99g and (262)Ha were unambiguously identified after gas chromatographic separa tion by measuring the characteristic gamma-lines of Nb-99g and by regi stering (262)Ha-Lr-258 mother-daughter alpha-alpha correlations as wel l as spontaneous fission decays, respectively. The adsorption enthalpi es of the investigated species on quartz surfaces were determined by a nalyzing the measured retention curves with a Monte Carlo model. Using an empirical correlation, the adsorption enthalpies were converted to sublimation enthalpies. The sublimation enthalpies of 95 +/- 16 kJ . mol(-1) and 124 +/- 16 kJ . mol(-1) determined for NbCl5 and NbOCl3, r espectively, were in good agreement with literature data. In experimen ts with Ha-chlorides a yield curve with two components was observed. S ublimation enthalpies of less than or equal to 120 kJ . mol(-1) and 15 2 +/- 18 kJ . mol(-1) were estimated for HaCl(5) and HaOCl(3), respect ively. The estimated sublimation enthalpies were compared with theoret ical predictions from relativistic calculations and with empirical ext rapolations of chemical properties. In agreement with empirical extrap olations, a lower volatility was found for HaOCl(3), than for NbOCl3.