# Magnetic tuning of ultracold barrierless chemical reactions

## TL;DR

This paper develops a theoretical framework to understand how magnetic fields influence ultracold barrierless chemical reactions, demonstrating potential control over reaction outcomes via hyperfine state tuning.

## Contribution

It introduces an extended coupled-channel statistical theory to analyze magnetic and hyperfine effects on ultracold reactions, applying it to a specific Li+CaH system.

## Key findings

- Large magnetic field effects on reaction cross sections.
- Potential for controlling reactions by tuning hyperfine states.
- Application to a specific Li+CaH reaction with ab initio potentials.

## Abstract

While attaining external field control of bimolecular chemical reactions has long been a coveted goal of physics and chemistry, the role of hyperfine interactions and dc magnetic fields in achieving such control has remained elusive. We develop an extended coupled-channel statistical theory of barrierless atom-diatom chemical reactions, and apply it to elucidate the effects of magnetic fields and hyperfine interactions on the ultracold chemical reaction Li($^2\text{S}_{1/2}$) + CaH($^2\Sigma^+$) $\to$ LiH($^1\Sigma^+$) + Ca($^1\text{S}_{0}$) on a newly developed set of ab initio potential energy surfaces. We observe large field effects on the reaction cross sections, opening up the possibility of controlling ultracold barrierless chemical reactions by tuning selected hyperfine states of the reactants with an external magnetic field.