Electron-impact rotational excitation of dipolar asymmetric top molecular ions

The reliability of astrochemical models depends largely on an accurate understanding of the underlying chemical processes that inform our ability to interpret observations.

This includes formation and destruction mechanisms, but also non-destructive inelastic collisions.

One such process is that of electron-impact rotational (de-)excitation of molecules.

Rotational excitation rates can be used to trace physically distinct regions in objects like planetary nebulae, and accurate rates are needed to keep pace with rapidly developing observational capabilities.

Additionally, such rates are also used in ground-based experiments to accurately infer the internal state distribution of molecules while making measurements.

Although rotationally resolved electron-impact collisions have been studied for several systems, molecular ions have received comparatively little treatment when compared to their neutral counterparts.

However, molecular ions are key tracers of physical parameters in various astrochemical environments, and especially so in diffuse media where the kinetic temperature is too low for neutral-neutral reactions to take place efficiently.

To address this, we have developed a theoretical approach that combines the power of R-matrix scattering theory, multichannel quantum defect theory, and frame transformation theory to accurately determine low-energy electron-impact rotational (de-)excitation rates for a general asymmetric molecule (ion or neutral), both with and without a significant dipole moment.