Bond energies of ThO+ and ThC+: A guided ion beam and quantum chemical investigation of the reactions of thorium cation with O2 and CO

Abstract

Kinetic-energy dependent reactions of Th⁺ with N₂ and NO are studied using a guided ion beam tandem mass spectrometer. The formation of ThO⁺ in the reaction of Th⁺ with NO is observed to be exothermic and barrierless with a reaction efficiency at low energies of 0.91 ± 0.18. Formation of ThN⁺ in the reactions of Th⁺ with N₂ and NO is endothermic in both cases. The kinetic-energy dependent cross sections for formation of this product ion were evaluated to determine a 0 K bond dissociation energy (BDE) of D₀(Th⁺-N) = 6.51 ± 0.08 eV, the first direct measurement of this BDE. Additionally, the reactions were explored by quantum chemical calculations, including a full Feller-Peterson-Dixon composite approach with correlation contributions up to CCSDTQ for ThN and ThN⁺, as well as more approximate CCSD(T) calculations where a semiempirical model was used to estimate spin-orbit energy contributions. The ThN⁺ BDE is found to be larger than those of the transition metal congeners, TiN⁺ along with estimated values for ZrN⁺ and HfN⁺, believed to be a result of the actinide contraction.