Dissociative recombination of cold HeH$^+$ ions

TL;DR

This paper presents a novel theoretical approach to model the dissociative recombination of cold HeH$^+$ ions, achieving good agreement with experimental data by combining multichannel quantum-defect theory, exterior complex scaling, and ab initio R-matrix calculations.

Contribution

It introduces the first application of energy-dependent frame transformation theory to dissociative recombination, integrating advanced quantum defect and R-matrix methods for accurate rate predictions.

Findings

Theoretical DR rates match experimental measurements.

The model successfully captures energy dependence of the process.

First application of this combined theoretical approach to HeH$^+$.

Abstract

The HeH$^+$ cation is the simplest molecular prototype of the indirect dissociative recombination (DR) process that proceeds through electron capture into Rydberg states of the corresponding neutral molecule. This Letter develops the first application of our recently developed energy-dependent frame transformation theory to the indirect DR processes. The theoretical model is based on the multichannel quantum-defect theory with the vibrational basis states computed using exterior complex scaling (ECS) of the nuclear Hamiltonian. The ab initio electronic R-matrix theory is adopted to compute quantum defects as functions of the collision energy and of the internuclear distance. The resulting DR rates are convolved over the beam energy distributions relevant to a recent experiment at the Cryogenic Storage Ring, giving good agreement between the experiment and the theory.