title: Thorium and uranium carbide cluster cations in the gas phase: similarities and differences between thorium and uranium.
abstract: Laser ionization of AnC4 alloys (An = Th, U) yielded gas-phase molecular thorium and uranium carbide cluster cations of composition An(m)C(n)(+), with m = 1, n = 2-14, and m = 2, n = 3-18, as detected by Fourier transform ion-cyclotron-resonance mass spectrometry. In the case of thorium, Th(m)C(n)(+) cluster ions with m = 3-13 and n = 5-30 were also produced, with an intriguing high intensity of Th13C(n)(+) cations. The AnC13(+) ions also exhibited an unexpectedly high abundance, in contrast to the gradual decrease in the intensity of other AnC(n)(+) ions with increasing values of n. High abundances of AnC2(+) and AnC4(+) ions are consistent with enhanced stability due to strong metal-C2 bonds. Among the most abundant bimetallic ions was Th2C3(+) for thorium; in contrast, U2C4(+) was the most intense bimetallic for uranium, with essentially no U2C3(+) appearing. Density functional theory computations were performed to illuminate this distinction between thorium and uranium. The computational results revealed structural and energetic disparities for the An2C3(+) and An2C4(+) cluster ions, which elucidate the observed differing abundances of the bimetallic carbide ions. Particularly noteworthy is that the Th atoms are essentially equivalent in Th2C3(+), whereas there is a large asymmetry between the U atoms in U2C3(+).
authors.affiliation: Unidade de Ciências Químicas e Radiofarmacêuticas, IST/ITN, Instituto Superior Técnico, Universidade Técnica de Lisboa , 2686-953 Sacavém, Portugal.
authors.forename: Cláudia C L
authors.initials: CC
authors.lastname: Pereira
authors.forename: Rémi
authors.initials: R
authors.lastname: Maurice
authors.forename: Ana F
authors.initials: AF
authors.lastname: Lucena
authors.forename: Shuxian
authors.initials: S
authors.lastname: Hu
authors.forename: António P
authors.initials: AP
authors.lastname: Gonçalves
authors.forename: Joaquim
authors.initials: J
authors.lastname: Marçalo
authors.forename: John K
authors.initials: JK
authors.lastname: Gibson
authors.forename: Lester
authors.initials: L
authors.lastname: Andrews
authors.forename: Laura
authors.initials: L
authors.lastname: Gagliardi