New approach characterizes electronic angular momentum decoupling schemes of autoionized ions

Electronic structure and angular momentum couplings in open-shell species are important factors to consider in elementary chemical processes such as those occurring in thermal plasmas and electrical discharges. Precise mechanisms behind the autoionization that could create these species, however, remain a topic of open inquiry. New work characterizing transient quasi-molecular species formed in autoionization processes provides a new path forward for understanding such fundamental reactions.

Falcinelli et al. have demonstrated a novel methodology that has allowed them to study electronic angular momentum decoupling schemes of autoionized krypton and xenon atoms by colliding them with excited but metastable neon atoms. Using a crossed molecular beam and a mass spectrometer and hemispherical electron analyzer as detectors, the authors were able to determine electron rearrangements and angular momentum coupling effects during collisions involving transient quasi-molecular species formed from such reactions, commonly referred to as the transition state.

The technique is able to provide information on the geometrical configuration assumed by the reacting species and its energy in addition to characterizing so-called Coriolis coupling effects.

The authors classified the properties of the autoionization processes as adiabatic and non-adiabatic. Adiabatic effects control sequence, energy and symmetry of quantum states accessible both to reactants and products, while non-adiabatic effects are responsible for triggering the passage from entrance to exit channels.

The work’s results are poised to help create a unifying theoretical picture for autoionization processes and for other chemical processes. The authors said that they next look to use their technique to further explore the stereodynamics of state-to-state autoionization reactions.

Source: “The electron couplings in the transition states: The stereodynamics of state to state autoionization processes,” by Stefano Falcinelli, Franco Vecchiocattivi, and Fernando Pirani, The Journal of Chemical Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5051174 .