Mechanism and Energetics of the Hydrolysis of Th+ To Form Th(OD)3+: Guided Ion Beam and Theoretical Studies of ThO+, ThO2+, and OThOD+ Reacting with D2O.

Abstract

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 (CID) 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 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 (BDEs) 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.