Dynamics of carbene formation in the reaction of methane with the tantalum cation in the gas phase.

Abstract

Using a crossed-beam velocity map imaging apparatus designed for transition-metal ion–molecule reactions, this study examined the gas-phase interaction between the tantalum cation (Ta⁺) and methane. Ta⁺ is among the rare atomic transition-metal cations capable of activating methane at room temperature, producing TaCH⁺ and molecular hydrogen via C–H bond cleavage. The reaction proceeds through intersystem crossing from the quintet to the triplet potential energy surface, a hallmark of multi-state reactivity common in transition-metal chemistry. Collision-energy-dependent differential cross sections were measured and compared with minimum energy pathway calculations. Analysis of TaCH⁺ velocity distributions revealed contributions from both indirect and rebound scattering dynamics. These findings were further contextualized by comparison with the previously studied oxygen-transfer reaction between Ta⁺ and carbon dioxide.

Mechanism

Ta⁺ activates the C–H bond of methane through multi-state reactivity involving intersystem crossing from the quintet to the triplet potential energy surface, yielding a tantalum carbene cation (TaCH⁺) and molecular hydrogen.