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

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Reactions of CO2 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+ + CO2 were examined using GIBMS. Modeling the kinetic energy-dependent GIBMS data allowed the determination of bond dissociation energies (BDEs) for D0(Th+-O) and D0(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 CO2 occur. As a consequence, both AnO+ and AnO2+ 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 AnOn+ (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 CO2 (a formally spin-forbidden reaction for most M+ ground states) and O2 (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+ + CO2 reaction efficiencies with the promotion energy (Ep) to the first electronic state with two valence d-electrons (Ep(5d2) for Ln+ and Ep(6d2) for An+) indicates that the primary limitation in the activation of CO2 is the energetic cost to promote from the electronic ground state of the atomic metal ion to a reactive state.