Dynamics of CO₂ activation by transition metal ions - The importance of intersystem crossing

Understanding chemistry at this level will help us to derive detailed structure reactivity relations with the final aim at controlling chemical reactivity using a bottom-up approach. We use gas phase methods to study the intrinsic atomistic dynamics of chemical reactions, i.e. how atoms rearrange during the chemical reaction. The energetics along the reaction coordinate are important and the influence of barriers is often used to predict the outcome of a reaction. However, in small systems, especially in gas phase, submerged barriers with respect to reactants can exert a profound influence on the reactivity in general and also the dynamics [1]. We use the combination of crossed beam with 3D velocity map imaging to gain insights into the dynamics of ion-molecule reactions [2,3]. The experimental angle and energy differential cross sections let us derive information on the collision geometry and the energy partitioning during the reaction.

Here, we present a joint experimental and theoretical study on the possible effects of intersystem crossing on the dynamics of transition metal ion-molecule reactions. Recent crossed beam imaging experiments in our group on the dynamics on oxygen atom transfer (OAT) reaction Ta⁺/Nb⁺ + CO2 → TaO⁺ + CO showed dominantly indirect dynamics [4,5,6] despite the thermal rates being close to collision rate and the reaction being highly exothermic [7,8]. The reaction of the OAT reaction between Ta⁺ and CO₂ is of multi-state character with the reaction crossing from the quintet surface to the triplet surface in the course of the reaction [9]. The question to the nature of the bottleneck along the reaction coordinate arose: A submerged transition state or the intersystem crossing. A combination of differential cross sections, thermal rate constants and high-level theory including trajectory calculations for the OAT for Ta⁺ and its lighter homologue niobium Nb⁺ could shed some more light on the question.

References

[1] H. Song and H. Guo, 406, 3, ACS Phys. Chem. Au (2023).

[2] R. Wester, 396, 16, Phys. Chem. Chem. Phys. (2014).

[3] J. Meyer and R. Wester, 333, 68, Annu. Rev. Phys. Chem. (2017)

[4] M. E. Huber et al., 8670, 26, Phys. Chem. Chem. Phys. (2024)

[5] M. Meta et al., 5524, 14, J. Phys. Chem. Lett. (2023)

[6] Y. Liu et. al., J. Am Chem. Soc. adv. online, doi: 10.1021/jacs.4c03192 (2024)

[7] G. K. Koyanagi and D. K. Bohme, 1232, 110, J. Phys. Chem. A (2006)

[8] M. R. Sievers and P. B. Armentrout, 103, 179, Int. J. Mass. Spectrom. (1998)

[9] D. Schröder, 139, 33, Acc. Chem. Res. (2000)