Add time:07/28/2019         Source:sciencedirect.com

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 AnO2 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 Sen+ clusters with n=2–9; the abundance distribution is compared with the high-temperature Sen equilibrium vapor composition. Several types of molecular and cluster ions were synthesized during the ablation process. Binary metal selenides, MSen+ (n>1), presumably formed primarily via electrostatic attraction between co-ablated Sen and M+. The compositions of binary metal oxide clusters, MxOm+ (x≤5) reflected the distinctive oxidation chemistries of the constituent metals. For the LnxOm+, LuIII was the highest oxidation state, whereas for AnxOm+, oxidation states up to UVI 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 MOy, MOy+, Sen and Sen+ is promoted. Among the most abundant clusters were AnOmSen+, the compositions of most of which suggested aggregation of AnOm+ with Sen. The compositions of some AnOmSen+ indicated Se2− ions in analogy with O2−; thus, AnSe+ and AnOSe+ were produced along with AnO+ and AnO2+, whereas both AnO2Se+ and AnO3+ were absent. The compositions of other AnOmSen+, such as PuO3Se+, 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 UO2 and Lu2O3. 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.

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