Electronic Structure Across the Periodic Table: Chemistry of the Large in Mass and the Small in Size

The results of several investigations are presented in this work. Each project results from research using applied theoretical simulations and electronic structure programs to elucidate and understand several difficult and complex problems from the bottom to the top of the periodic table. Work within each of these projects contain efforts to understand ground, low-lying(≤ 2eV) or highly excited(≥ 500eV) electronic states.

Reactions involving the thorium analog to ferrocene ([Cp₂Th]²⁺) were studied, using relativistic effective core potentials and density functional theory, to explore the accessibility of linear thorocene from Cp^∗₂Th^IVL_n complexes. Newly predicted ground-state structures of the form Cp₂Th^IVL_n where n = 1-5 are reported, where L =[F]⁻, [Cl]⁻, [Br]⁻, [I]⁻, H₂O, [NH₂]⁻, [NCS]⁻, NCMe,[CN]⁻, [CHCH₂]⁻, [CH₃]⁻, CO and pyridine N-oxide. With the exception of the amido complexes, all ground states contain a linear Cp₂Th unit. The requirements for forming linear actinocene moieties are discussed in light of current results and existing experimental efforts with uranium metallocene complexes.

The activation of small (C₁-C₄) alkanes and alkenes by bare and oxo-ligated actinide cations(Th⁺ through Cm⁺) has been systematically examined using Fourier transform ion cyclotron resonance mass spectrometry. The reactivity trend identified for the highly reactive early actinide ions, Th⁺ > Pa⁺ > U⁺ > Np⁺, is interpreted to indicate significant 5f electron participation in organoactinide σ-type bond formation for Pa⁺. Among the seven studied AnO⁺ ions, only ThO⁺, PaO⁺, and UO⁺ activated at least one hydrocarbon, with the reactivity of PaO⁺ being distinctively high. Electronic structure calculations for PaO⁺ show that its ground state is [Pa(5f6d)O]⁺, i.e., with one 5f and one 6d nonbonding electrons available on the metal, and all of its excited states up to 1.8 eV have a 5f orbital occupancy of ≥0.8. The high reactivity and substantial 5f character of PaO⁺ indicate participation of 5f electrons in hydrocarbon bond activation for oxo-ligated Pa⁺. The results of this work reveal that 5f electrons play a distinctive role in protactinium chemistry involving σ-type organometallic bonding.

The lower energy levels of the protactinium (Pa) atom are unusually difficult to treat theoretically. Pa is located where the 6d and 5f energies cross; simple calculations consistently put the electron configurations 5f¹6d²7s² and 5f²6d¹7s² in the incorrect order. We have used multireference spin-orbit configuration interaction to compute the energies of these states to determine which additional interactions need to be included. We also discuss the less common J₁j coupling scheme suggested for these atomic states with applications also to the 5f¹6d² and 5f²6d¹ states of Pa²⁺.

The core-excitation of electrons and formation of valence resonance states were determined for the water monomer and attempted for dimer. Excitation energy for removal of an electron from the oxygen 1s type atomic orbital to the available anti-bonding valence orbitals is modeled using spin-orbit configuration interaction with single and double excitations. Initial determinations of excitation energy, oscillator strengths and transition dipole magnitudes were obtained. The oscillator strengths for transitions in the dimer appear to show a dependence on the molecular orbital density localization.