# Long-range vs. short-range effects in cold molecular ion-neutral collisions: Charge exchange of Rb with N$_2^+$ and O$_2^+$

## TL;DR

This study investigates charge-transfer reactions between Rb atoms and molecular ions N$_2^+$ and O$_2^+$ at millikelvin temperatures, revealing the influence of both short- and long-range interactions on reaction dynamics through experimental and theoretical analysis.

## Contribution

It provides a detailed experimental and theoretical analysis of charge-transfer reactions at ultracold temperatures, highlighting the interplay of short- and long-range effects in different reaction channels.

## Key findings

- Reaction rates vary with collision energy and state.
- Different reaction channels exhibit distinct kinetic behaviors.
- Short-range interactions involve complex multi-collision processes.

## Abstract

We report a study of cold charge-transfer (CT) collisions of Rb atoms with N$_2^+$ and O$_2^+$ ions in the mK regime using a dynamic ion-neutral hybrid trapping experiment. State- and collision-energy- dependent reaction rate coefficients have been measured for both systems. We observe markedly different charge-transfer kinetics and dynamics for the different systems and reaction channels. While the kinetics in some channels are consistent with classical capture theory for the rate coefficient, others show distinct non-universal dynamics. The experimental results are interpreted with the help of classical capture, quasiclassical trajectory and quantum scattering calculations using state-of-the-art ab-initio potentials for the highly excited molecular states involved. The theoretical analysis reveals an intricate interplay between short- and long-range effects in the different reaction channels which ultimately determines the CT dynamics and rates. At short range, CT was found to occur via both single and multiple collision events with the latter typically showing pronounced large-amplitude internal motions of the collision complex. Our results illustrate salient mechanisms that determine the efficiency of cold molecular CT reactions.