Praseodymium cation (Pr+) reactions with H2, D2, and HD: PrH+ bond energy and mechanistic insights from guided ion beam and theoretical studies

Guided ion beam tandem mass spectrometry was used to study the reactions of the atomic lanthanide praseodymium cation (Pr+) with H2, D2, and HD as a function of collision energy. Modeling the kinetic-energy-dependent endothermic reactions to form PrH+ (PrD+) yields a 0 K bond dissociation energy (BDE) of 2.10 ± 0.05 eV for PrH+. Quantum chemical calculations were performed for PrH+ at the B3LYP, BHLYP, PBE0, and coupled-cluster with single, double, and perturbative triple levels of theory, and they overestimate the PrH+ experimental BDE by 0.06 –0.28 eV. The branching ratio of the PrH+ and PrD+ products in the HD reaction suggests that the reaction occurs via a direct reaction mechanism with short-lived intermediates. This is consistent with the theoretical calculations for the relaxed potential energy surfaces of PrH2+, where no strongly bound dihydride intermediates were found. The reactivity and PrH+ BDE are compared with previous results for lanthanide metal cations (La+, Ce+, Sm+, Gd+, and Lu+). Periodic trends across the lanthanide series and insights into the role of the electronic configuration on metal-hydride bond strength are discussed.