Elucidating cerium + H₂O reactivity through electronic structure: A combined PES and DFT study

The anion photoelectron (PE) spectra of Ce_xO_yH_z⁻ products formed in sequential reactions between cerium oxide and hydroxide reactions with water are presented and interpreted with supporting density functional theory calculations. The PE spectra of Ce_xO_yH_z⁻ (x = 2, 3) complexes formed in the sequence of reactions initiated with Ce_xO_x⁻ + H₂O, exhibit a prominent photodetachment transition indicating that the highest occupied molecular orbital in these species can be described as combinations of Ce 6s atomic orbitals. The electrons in these diffuse orbitals reliably have low binding energies in the range of 0.6–1 eV. The combination of poor orbital overlap and low binding energy is amenable to ionic Ce[sbnd]OH bond formation in reactions with water, rather than Ce[dbnd]O bond formation, which is observed in more reduced clusters that have occupied Ce 5d-based molecular orbitals. Spectral simulations based on computational results, which predict numerous close-lying spin states arising from the singly occupied 4f orbital on each Ce center, support specific structural assignments for the Ce₂O_yH_z⁻ cluster series. A range of Ce₃O_yH_z⁻ products also exhibit the characteristic Ce 6s-based MO photodetachment transition. Based on comparison with calculations that predict stable cerium hydride structures, we infer that the sequence of Ce₃O_yH_z⁻ + H₂O reactions proceeds along a path of metastable structures.