Activation of CO by Actinide Cations (Th, U, Pu, and Am) as Studied by Guided Ion Beam and Triple Quadrupole Mass Spectrometry.

Reactions of CO with Th have been studied using guided ion beam tandem mass spectrometry (GIBMS) and with An (An = Th, U, Pu, and Am) using triple quadrupole inductively coupled plasma mass spectrometry (QQQ-ICP-MS). Additionally, the reactions ThO + CO and ThO + CO were examined using GIBMS. Modeling the kinetic energy-dependent GIBMS data allowed the determination of bond dissociation energies (BDEs) for (Th-O) and (OTh-O) that are in reasonable agreement with previous GIBMS measurements. The QQQ-ICP-MS reactions were studied at higher pressures where multiple collisions between An and the neutral CO occur. As a consequence, both AnO and AnO products were observed for all An except Am, where only AmO was observed. The relative abundances of the observed monoxides compared to the dioxides are consistent with previous reports of the AnO ( = 1, 2) BDEs. A comparison of the periodic trends of the group 4 transition metal, lanthanide (Ln), and actinide atomic cations in reactions with CO (a formally spin-forbidden reaction for most M ground states) and O (a spin-unrestricted reaction) indicates that spin conservation plays a minor role, if any, for the heavier Ln and An metals. Further correlation of Ln and An + CO reaction efficiencies with the promotion energy () to the first electronic state with two valence -electrons ((5d) for Ln and (6d) for An) indicates that the primary limitation in the activation of CO is the energetic cost to promote from the electronic ground state of the atomic metal ion to a reactive state.