Mechanism and Energetics of the Hydrolysis of Th⁺ To Form Th(OD)₃⁺ : Guided Ion Beam and Theoretical Studies of ThO⁺, ThO ₂⁺, and OThOD ⁺ Reacting with D₂O

The kinetic energy dependences of the reactions of ThO⁺, ThO₂⁺, and OThOD⁺ with D₂O, ThO₂⁺ with D₂, and OThOD⁺ with Xe were studied using guided ion beam tandem mass spectrometry. Exothermic formation of OThOD⁺ is the dominant process observed in reactions of both ThO⁺ and ThO₂⁺ with D₂O. Minor products formed in endothermic reactions include ThO₂⁺, DThO⁺, and ThO₂D₂⁺. OThOD⁺ is also formed in the reaction of ThO₂⁺ with D₂ but in an endothermic process. Collision-induced dissociation of OThOD⁺ with Xe leads to endothermic loss of the hydroxide ligand. OThOD⁺ reacts further with D₂O to form the associative complex ThO₃D₃⁺, which is long-lived before dissociating back to the reactants. The OThOD⁺ D₂O bond energy of the associative complex is measured to be 2.96 ± 0.05 eV by modeling the kinetic energy dependent cross section for association using a phase space theory (PST) model that rigorously conserves angular momentum. By comparison with theory, this bond energy identifies the ThO₃D₃⁺ species as the trihydroxide cation, Th(OD)₃⁺. From the endothermic reactions and CID of OThOD⁺ with Xe, the OTh⁺-D, OTh⁺ -O, and OTh⁺ -OD bond dissociation energies are measured to be 2.33 ± 0.24, 4.66 ± 0.15, and 6.00 ± 0.17 eV, respectively. All four of these BDEs are experimentally determined for the first time and agree reasonably well with values calculated at the B3LYP, B3PW91, and PBE0 levels of theory with cc-pVQZ basis sets. Complete potential energy surfaces for all reactions were calculated at the B3LYP/cc-pVTZ level and elucidate the mechanisms for all processes observed.