Guided Ion Beam Studies of the Thorium Monocarbonyl Cation Bond Dissociation Energy and Theoretical Unveiling of Different Isomers of [Th,O,C]+ and Their Rearrangement Mechanism

Threshold collision-induced dissociation (TCID) of the thorium monocarbonyl cation, ThCO+, with xenon is performed using a guided ion beam tandem mass spectrometer. The only product observed is Th+ resulting from loss of the CO ligand. Analysis of the kinetic energy-dependent cross sections for this CID reaction yields the first experimental determination of the bond dissociation energy (BDE) of Th+–CO at 0 K as 0.94 ± 0.06 eV. Calculated BDEs at the CCSD­(T) level of theory with cc-pVXZ (X = T and Q) basis sets and a complete basis set (CBS) extrapolation are in good agreement with the experimental result. The Feller–Peterson–Dixon composite coupled-cluster methodology was also applied on both ThCO+ and ThCO, with contributions up to CCSDT­(Q) and a four-component treatment of spin–orbit coupling effects. The final 0 K Th+–CO BDE of 0.94 ± 0.04 eV is in excellent agreement with the current experimental result. The ionization energy of ThCO, as well as the atomization energies and heats of formation for both ThCO and ThCO+, is reported at this same level of theory. Complete potential energy profiles of both quartet and doublet spin are also constructed to elucidate the mechanism for the formation and interconversion of different isomers of [Th,O,C]+. Chemical bonding patterns in low-lying states of ThCO+ and potential energy curves for ThCO+ dissociation are also investigated.