ToF-SIMS characterization of uranium hydride

Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) has been employed for the first time to investigate uranium hydride. The deuterated form of uranium hydride (UD3) was formed on a polycrystalline uranium sample by exposure to high-purity D-2 gas at room temperature. The characteristic positive and negative secondary-ion fragments observed from uranium hydride are reported and assigned. Our investigations show that negative-ion fragments provide the most unambiguous method for identification of uranium hydride, through the detection of UH2- and UH4- fragments. In addition, density functional theory (DFT) calculations are presented which confirm the identity and stability of, and also assign structural geometries to, the ion fragments observed within the SIMS experiment. The DFT calculations show that UH2+/- ions adopt a linear arrangement, whereas positive tri- and tetrahydride ions ( UH3+, UH4+) adopt structures based on square planar geometries, although negative tri- and tetrahydride ions (UH3-, UH4-) adopt structures based on tetrahedral geometries.