f-Block reactions of metal cations with carbon dioxide studied by inductively coupled plasma tandem mass spectrometry.

f-Block chemistry offers an opportunity to test current knowledge of chemical reactivity. The energy dependence of lanthanide cation (Ln + = Ce + , Pr + , Nd + -Eu + ) and actinide cation (An + = Th + , U + -Am + ) oxidation reactions by CO 2 , was observed by inductively coupled plasma tandem mass spectrometry. This reaction is commonly spin-unallowed because the neutral reactant (CO 2 , 1 Σ+g) and product (CO, 1 Σ + ) require the metal and metal oxide cations to have the same spin state. Correlation of the promotion energy ( E p ) to the first state with two free d-electrons with the reaction efficiency indicates that spin conservation is not a primary factor in the reaction rate. The E p likely influences the reaction rate by partially setting the crossing between the ground and reactive states. Comparison of Ln + and An + congener reactivity indicates that the 5f-orbitals play a small role in the An + reactions.