Laser ablation synthesis of actinide selenide, oxide and oxide–selenide clusters: AnSen+, AnxOm+ and AnxOmSen+ [An=U, Np, Pu

Abstract

Abstract Actinide (An=U, Np, Pu) selenide, oxide and oxide–selenide molecular and cluster cations were synthesized by pulsed laser ablation of targets consisting of dilute mixtures of AnO 2 in a selenium matrix; selected lanthanides (Ln=Ho, Tm, Lu) were included for comparison. The compositions and abundance distributions of the molecules/clusters reflected distinctive f-element chemistries. Ablation of pure selenium resulted in Se n + clusters with n =2–9; the abundance distribution is compared with the high-temperature Se n equilibrium vapor composition. Several types of molecular and cluster ions were synthesized during the ablation process. Binary metal selenides, MSe n + ( n >1), presumably formed primarily via electrostatic attraction between co-ablated Se n and M + . The compositions of binary metal oxide clusters, M x O m + ( x ≤5) reflected the distinctive oxidation chemistries of the constituent metals. For the Ln x O m + , Lu III was the highest oxidation state, whereas for An x O m + , oxidation states up to U VI were exhibited. The formation of binary selenides and oxide clusters is attributed to the high volatility of selenium, which results in a dense ablation plume in which coalescence of MO y , MO y + , Se n and Se n + is promoted. Among the most abundant clusters were AnO m Se n + , the compositions of most of which suggested aggregation of AnO m + with Se n . The compositions of some AnO m Se n + indicated Se 2− ions in analogy with O 2− ; thus, AnSe + and AnOSe + were produced along with AnO + and AnO 2 + , whereas both AnO 2 Se + and AnO 3 + were absent. The compositions of other AnO m Se n + , such as PuO 3 Se + , indicated O–Se bonding, such as occurs in selenites. The feasibility of synthesis of metal oxide cluster ions by co-ablation of oxides and poly(acrylic acid) was assessed for UO 2 and Lu 2 O 3 . Oxide clusters were produced in appreciable quantities, but interpretation of the results was complicated by formation of complex ions from reactions with polymer fragments. Ablation of OH radicals resulted in species comprising M-(OH) as well as M=O moieties, the masses of which were often too similar to allow for definitive differentiation.