Gas-phase chemistry of technetium carbonyl complexes

Abstract

Gas-phase chemical behaviors of short-lived technetium carbonyl complexes were studied using a low temperature isothermal chromatograph (IC) coupled with a ²⁵²Cf spontaneous fission (SF) source. Fission products recoiled from the ²⁵²Cf SF source were thermalized in a mixed gas containing CO, and then technetium carbonyl complexes were formed from reactions between CO gas and various technetium isotopes. A gas-jet system was employed to transport the volatile carbonyl complexes from a recoil chamber to the IC. Short IC columns made of Fluorinated Ethylene Propylene (FEP) Teflon and quartz were used to obtain chemical information about the technetium carbonyl complexes. The results for the ¹⁰⁴Tc–¹⁰⁶Tc carbonyl complexes were found to be strongly influenced by the precursors, and showed the chemical behaviors of ¹⁰⁴Mo–¹⁰⁶Mo carbonyl complexes, respectively. However, ¹⁰⁷Tc and ¹⁰⁸Tc could represent the chemical information of the element technetium due to their high independent yields and the very short half-lives of their precursors ¹⁰⁷Mo and ¹⁰⁸Mo. An adsorption enthalpy of about ΔH_ads = −43 kJ mol⁻¹ was determined for the Tc carbonyl complexes on both the Teflon and quartz surfaces by fitting the breakthrough curves of the ¹⁰⁷Tc and ¹⁰⁸Tc carbonyl complexes with a Monte Carlo simulation program. Chemical yields of around 25% were measured for the Tc carbonyl complexes relative to the transport yields obtained with the gas-jet transport of KCl aerosol particles with Ar carrier gas. Furthermore, the influence of a small amount of O₂ gas on the yields of the Mo and Tc carbonyl complexes was studied.