Activation of CO2 by Actinide Cations (Th+, U+, Pu+, and Am+) as Studied by Guided Ion Beam and Triple Quadrupole Mass Spectrometry

Reactions of CO 2 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 2 were examined using GIBMS. Modeling the kinetic energy-dependent GIBMS data allowed the determination of bond dissociation energies (BDEs) for D 0 (Th + –O) and D 0 (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 2 occur. As a consequence, both AnO + and AnO 2 + 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 n + ( n = 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 2 (a formally spin-forbidden reaction for most M + ground states) and O 2 (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 2 reaction efficiencies with the promotion energy ( E p ) to the first electronic state with two valence d -electrons ( E p (5d 2 ) for Ln + and E p (6d 2 ) for An + ) indicates that the primary limitation in the activation of CO 2 is the energetic cost to promote from the electronic ground state of the atomic metal ion to a reactive state.