Evaluation of the exothermicity of the chemi-ionization reaction Nd + O → NdO+ + e- and neodymium oxide, carbide, dioxide, and carbonyl cation bond energies.

Abstract

The exothermicity of the chemi-ionization reaction, Nd + O → NdO+ + e-, has been indirectly determined by measuring the thermochemistry for reactions of the lanthanide metal neodymium cation (Nd+) with O2, CO2, and CO and reactions of NdO+ with CO, O2, and Xe. Guided ion beam tandem mass spectrometry was used to measure the kinetic energy dependent product ion cross sections for these reactions. NdO+ is formed through a barrierless exothermic process when the atomic metal cation reacts with O2 and CO2. 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 several species. The 0 K BDE for Nd+-O is determined to be 7.28 ± 0.10 eV from the average of four independent thresholds. This value is combined with the well-established Nd ionization energy to indicate an exothermicity of the title reaction of 1.76 ± 0.10 eV, which is lower and more precise than literature values. In addition, the Nd+-C, ONd+-O, and Nd+-CO BDEs are determined to be 2.61 ± 0.30, 2.12 ± 0.30, and 0.30 ± 0.21 eV. Additionally, theoretical BDEs of Nd+-O, Nd+-C, ONd+-O, and Nd+-CO are calculated at several levels for comparison with the experimental values. B3LYP calculations seriously underestimate the Nd+-O BDE, whereas MP2 and coupled-cluster with single, double-and perturbative triple excitations values are in reasonable agreement. Good agreement is generally obtained for Nd+-C, ONd+-O, and Nd+-CO BDEs as well.