Electronic Properties of UN and UN - from Photoelectron Spectroscopy and Correlated Molecular Orbital Theory.

The results of calculations of the properties of the anion UN ^- including electron detachment are described, which further expand our knowledge of this diatomic molecule. High-level electronic structure calculations were conducted for the UN and UN ^- diatomic molecules and compared to photoelectron spectroscopy measurements. The low-lying Ω states were obtained using multireference CASPT2 including spin-orbit effects up to ∼20,000 cm ^-1 . At the Feller-Peterson-Dixon (FPD) level, the adiabatic electron affinity (AEA) of UN is estimated to be 1.402 eV and the vertical detachment energy (VDE) is 1.423 eV. The assignment of the UN excited states shows good agreement with the experimental results with a VDE of 1.424 eV. An Ω = 4 ground state was obtained for UN ^- which is mainly associated with the ³ H ΛS state. Thermochemical calculations estimate a bond dissociation energy (BDE) for UN ^- (U ^- + N) of 665.9 kJ/mol, ∼15% larger than that of UN and UN ⁺ . The NBO analysis reveals U-N triple bonds for the UN, UN ^- , and UN ⁺ species.