Enthalpy of the Cerium (Ce) Chemi-Ionization Reaction and CeO, CeC, and CeCO Bond Energies Determined by Energy-Resolved Guided Ion Beam Mass Spectrometry Experiments.

Cerium (Ce) oxide, carbide, and carbonyl cation bond energies and the exothermicity of the Ce chemi-ionization (CI) reaction with atomic oxygen were investigated using guided-ion beam tandem mass spectrometry (GIBMS). The kinetic energy dependent product cross sections for reactions of Ce with O, CO, and CO and CeO with O, CO, Xe, and Ar were measured using GIBMS. For the reactions of Ce with O and CO, CeO is formed through an exothermic reaction, whereas CeO formation is endothermic in the reaction with CO. This reaction also forms CeC and CeCO is formed in the reaction of Ce with CO, both in endothermic processes. Reactions of CeO with all four gases led to endothermic collision-induced dissociation as well as exchange reactions to form CeO for the O and CO reactants. Bond dissociation energies (BDEs) at 0 K were determined through analyses of the kinetic energy dependent cross sections for all endothermic reactions. We determined that the BDEs of CeO, CeC, and CeCO are 8.46 ± 0.15, 3.93 ± 0.16, and ≥0.25 ± 0.07 eV, respectively, where the CeO BDE is a weighted average of 6 independent 0 K threshold measurements. The CeO BDE is combined with the ionization energy (IE) of Ce to determine an exothermicity of 2.91 ± 0.15 eV for the Ce + O → CeO + e chemi-ionization reaction. Combined with neutral BDEs from the literature, the thermochemistry determined here also provides IE(CeO) = 5.03 ± 0.12 eV and IE(CeC) = 6.50 ± 0.16 eV. Theoretical calculations for ground and some excited states were performed for CeO, CeC, and CeCO to provide insight into the bonding and a comparison with the experimentally determined BDEs for each molecule.