Dissociative recombination of rotationally cold ArH$^+$

TL;DR

This study experimentally investigates the dissociative recombination of cold ArH$^+$ ions, revealing the dominant pathways and providing data for astrochemical modeling, highlighting the importance of non-adiabatic couplings.

Contribution

First experimental measurement of DR rate coefficient for rotationally cold ArH$^+$, including internal state analysis of the products and comparison with theoretical models.

Findings

DR products are in ground states at low energies

Non-adiabatic couplings are crucial for the DR pathway

Derived rate coefficient for astrochemical models

Abstract

We have experimentally studied dissociative recombination (DR) of electronically and vibrationally relaxed ArH$^+$ in its lowest rotational levels, using an electron--ion merged-beams setup at the Cryogenic Storage Ring. We report measurements for the merged-beams rate coefficient of ArH$^+$ and compare it to published experimental and theoretical results. In addition, by measuring the kinetic energy released to the DR fragments, we have determined the internal state of the DR products after dissociation. At low collision energies, we find that the atomic products are in their respective ground states, which are only accessible via non-adiabatic couplings to neutral Rydberg states. Published theoretical results for ArH$^+$ have not included this DR pathway. From our measurements, we have also derived a kinetic temperature rate coefficient for use in astrochemical models.