Reactions of Atomic Thorium and Uranium Cations with SF Studied by Guided Ion Beam Tandem Mass Spectrometry.

The fundamental chemistry of the thorium and uranium fluorides continues to be an area of interest because of the use of thorium and uranium fluoride compounds in nuclear fuel systems. Here, we study the reaction of thorium cations with sulfur hexafluoride for the first time and revisit the reaction of uranium cations with sulfur hexafluoride. By using guided ion beam tandem mass spectrometry, we explore the reaction pathways that become accessible well above thermal energies ( ∼ 0.04 eV). Overall, we find that both Th and U react very efficiently with SF, approaching the collision limit at both thermal and elevated energies. The primary products observed at low energies include Th, UF, and SF, all of which are formed in barrierless, exothermic processes. SF was also observed, although the pressure dependence of this channel reveals that SF forms exothermically through secondary reactions, which the energy dependences suggest result from reactions between ThF and UF with SF. At higher energies, both AnF products are observed to decay to AnF + F, and both SF and SF exhibit cross sections with endothermic features. For both systems, the rise in SF can be attributed to a secondary collision between AnF with SF on the basis of the pressure dependence of the SF channel at higher energies, and the rise in SF appears to result from the decomposition of SF to SF + F.