Thermochemistry of Elementary Actinide Sulfide Molecules: A Gas-Phase Study of Curium Sulfide
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1264-Z02-04
Thermochemistry of Elementary Actinide Sulfide Molecules: A Gas-Phase Study of Curium Sulfide Cláudia C. L. Pereira1, Joaquim Marçalo1 and John K. Gibson2 1 Unidade de Ciências Químicas e Radiofarmacêuticas, Instituto Tecnológico e Nuclear, 2686953 Sacavém, Portugal 2 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA ABSTRACT Experiments to explore the reactivity and thermochemistry of elementary transuranium sulfide molecules have been initiated to expand the basis for a fundamental understanding of actinide bonding, and to enable the development of advanced theoretical methodologies which will be of general applicability to more complex molecular systems. Bimolecular gas-phase reactions between transuranium actinide ions and neutral reagents are employed to obtain thermochemical information. The initial actinide sulfide studies have focused on obtaining the 298 K bond dissociation energy for the CmS+ ion, D[Cm+-S] = 475±37 kJ mol-1; from this result and an estimate of IE[CmS] ≈ IE[CmO] + 0.5 eV, we obtain D[Cm-S] = 563±64 kJ mol-1. The bond dissociation energies, D[Cm+-S] and D[Cm-S] are approximately 200 kJ mol-1 and 150 kJ mol-1 lower than for the corresponding oxides, CmO+ and CmO. The nature of the bonding in the CmS+ ion appears to be generally similar to that in other oxophilic metal sulfides. Comparisons with previous bond dissociation energies reported for ThS and US may suggest a difference in the An-S bonds for these early actinide sulfides as compared with CmS. INTRODUCTION Gas-phase reactivity studies of bare and ligated actinide ions have been expanded in recent years to provide fundamental insights into key aspects of actinide chemistry, including the changing role of the 5f electrons in bonding across the actinide series.1,2,3 There has been a particular focus on the thermochemistry of elementary oxide molecules,4 which provides a basis to evaluate advanced theoretical methodologies, such as in the recent cases of dissociation energies of americium and curium oxides5 and ionization energies of plutonium oxides.6 Both the experiment and theory efforts need to be expanded to bonding between actinides and main group elements other than oxygen, to provide a sound fundamental basis to rationally control the behavior of actinides in the environment and in nuclear fuel cycle schemes. A particularly important current field in which enhanced understanding of bonding between actinides and coordinating ligands is for advanced separations processes.7 A key aspect of actinide chemistry in general, and actinide separations in particular, is the nature of interactions between actinide ions and “hard” versus “soft” chalcogen atoms.8 We have recently initiated a project to
experimentally study gas-phase reactions of actinide ions and sulfur-containing neutral molecules, with a central objective of obtaining key thermochemical quantities, particularly bond dissociation energies. An ultimate goal of this project is to provide as comprehensive a collection as feas
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