AbstractExperiments 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.