Reactions of Th+ + H2, D2, and HD Studied by Guided Ion Beam Tandem Mass Spectrometry and Quantum Chemical Calculations
2016
Cox, Richard M | Armentrout, P. B. | de Jong, Wibe A.
Kinetic energy dependent reactions of Th⁺ with H₂, D₂, and HD were studied using a guided ion beam tandem mass spectrometer. Formation of ThH⁺ and ThD⁺ is endothermic in all cases with similar thresholds. Branching ratio results for the reaction with HD indicate that Th⁺ reacts via a statistical mechanism, similar to Hf⁺. The kinetic energy dependent cross sections for formation of ThH⁺ and ThD⁺ were evaluated to determine a 0 K bond dissociation energy (BDE) of D₀(Th⁺–H) = 2.45 ± 0.07 eV. This value is in good agreement with a previous result obtained from analysis of the Th⁺ + CH₄ reaction. D₀(Th⁺–H) is observed to be larger than its transition metal congeners, TiH⁺, ZrH⁺, and HfH⁺, believed to be a result of lanthanide contraction. The reactions with H₂ were also explored using quantum chemical calculations that include a semiempirical estimation and explicit calculation of spin–orbit contributions. These calculations agree nicely and indicate that ThH⁺ most likely has a ³Δ₁ ground level with a low-lying ¹Σ⁺ excited state. Theory also provides the reaction potential energy surfaces and BDEs that are in reasonable agreement with experiment.
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