Cerium Cation (Ce + ) Reactions with H 2 , D 2 , and HD: CeH + Bond Energy and Mechanistic Insights from Guided Ion Beam and Theoretical Studies

Reactions of the atomic lanthanide cerium cation (Ce ) with H , D , and HD were studied by using guided ion beam tandem mass spectrometry. Analysis of the kinetic-energy-dependent endothermic reactions to form CeH (CeD ) led to a 0 K bond dissociation energy (BDE) for CeH of 2.19 ± 0.09 eV. Theoretical calculations for CeH were performed at the B3LYP, BHLYP, and PBE0 levels of theory and overestimate the experimental BDE. In contrast, extrapolation to the complete basis set limit using coupled-cluster with single, double, and perturbative triple excitations, CCSD(T), gave a value (2.33 eV) in reasonable agreement with the experimental BDE. The branching ratio of the CeH and CeD products in the HD reaction suggests that the reaction occurs via a statistical mechanism involving a long-lived intermediate. Relaxed potential energy surfaces for CeH were computed and are consistent with the availability of such an intermediate, but the crossing point between quartet and doublet surfaces helps explain the inefficiency of the association reaction observed in the literature. The reactivity and CeH BDE are compared with previous results for group 4 transition metal cations (Ti , Zr , and Hf ), other lanthanides (La , Sm , Gd , and Lu ), and the isovalent actinide Th . Periodic trends and insight into the role of the electronic configuration on metal-hydride bond strength are discussed.