Evaluation of the Pr + O → PrO+ + e− chemi-ionization reaction enthalpy and praseodymium oxide, carbide, dioxide, and carbonyl cation bond energies

Abstract

Guided ion beam tandem mass spectrometry (GIBMS) was used to measure the kinetic energy dependent product ion cross sections for reactions of the lanthanide metal praseodymium cation (Pr⁺) with O₂, CO₂, and CO and reactions of PrO⁺ with CO, O₂, and Xe. PrO⁺ is formed through barrierless exothermic processes when the atomic metal cation reacts with O₂ and CO₂, whereas all other reactions are observed to be endothermic. Analyses of the kinetic energy dependences of these cross sections yield 0 K bond dissociation energies (BDEs) for PrO⁺, PrC⁺, PrCO⁺, and PrO₂⁺. The 0 K BDE for PrO⁺ is determined to be 7.62 ± 0.09 eV from the weighted average of five independent thresholds. This value is combined with the well-established ionization energy (IE) of Pr to indicate an exothermicity of the chemi-ionization reaction, Pr + O → PrO⁺ + e⁻, of 2.15 ± 0.09 eV. Additionally, BDEs of Pr⁺–C, OPr⁺–O, and Pr⁺–CO are determined to be 2.97 ± 0.10. 2.47 ± 0.11, and 0.31 ± 0.07 eV. Theoretical Pr⁺–O, Pr⁺–C, OPr⁺–O, and Pr⁺–CO BDEs are calculated for comparison with experimental values. The Pr⁺–O BDE is underestimated at the B3LYP and PBE0 level of theory but better agreement is obtained using the coupled-cluster with single, double, and perturbative triple excitations, CCSD(T), level. Density functional theory approaches yield better agreement for the BDEs of Pr⁺–C, OPr⁺–O, and Pr⁺–CO.