IR spectra of uranium hydride molecules isolated in solid argon

Abstract

The primary reaction products of laser-ablated uranium atoms with dihydrogen (UH, UH2, U2H2, UH3 and UH4) are isolated for the first time in an argon matrix and identified by the effects of isotopic substitution on their IR spectra.

A Combined Experimental and Theoretical Study of Uranium Polyhydrides with New Evidence for the Large Complex UH4(H2)6

“…The DFT harmonic vibrational frequencies and their IR intensities for U 2 H 2 , U 2 H 4 , and U 2 H 6 and their deuterated isotopes are reported in Tables 1SI-3SI of the Supporting Information. In the case of U 2 H 6 , only the isotope in which all the six hydrogen were replaced by deuterium was considered.…”

“…A similar calculation on a single H 2 molecule predicts a bond distance of 0.75 Å, indicating that the H 2 moieties interact with the U atom to form a strong complex. The structure of UH 4 (H 2 ) 6 corresponds to a central UH 4 moiety surrounded by six H 2 molecules oriented along the tetrahedron edges. UH 4 (H 2 ) 6 is 0.56 eV lower in energy (including zero-point-energy correction) than UH 4 and six H 2 .…”

“…The weaker bands at 1565.0 and 1555.6 cm -1 are most likely due to the UH 4 symmetric stretching mode with infrared intensity in the complex. We considered these bands for UH 6 , but this unlikely molecule is 1.8 eV higher in energy than the UH 4 (H 2 ) complex, and earlier workers have suggested that UH 6 has a low barrier to exothermic dissociation 16,17 Experiments were done with 1, 4, and 6% H 2 in neon to look for concentration effects and more dramatic effects on annealing. We find that the 1494.7 cm -1 band is favored over the 1513.6 cm -1 band when concentration is increased and on annealing.…”

“…There is evidence of U-U bond from gas-phase experiments 5 or in U 2 H 2 species, experimentally trapped in argon matrices. 6,7 The primary reaction products of laser-ablated uranium atoms with dihydrogen (UH, UH 2 , UH 3 , UH 4 , and U 2 H 2 ) were isolated in solid argon and identified by the effects of isotopic substitution on their infrared spectra some time ago. 7 Density functional theory (DFT) calculations were also performed to provide theoretical support for the spectral assignment.…”

“…New experimental observations in solid hydrogen and neon will also be reported. In the attempt to identify the various species, the existence of a novel system, with formula UH 4 (H 2 ) 6 , was predicted. This supersystem has a potential interest as a novel metal hydride with a large number of hydrogens bound to a metal.…”