Spin-state-controlled chemi-ionization reactions between metastable helium atoms and ground-state lithium atoms

TL;DR

This study shows that controlling the spin states of metastable helium and ground-state lithium atoms can significantly influence chemi-ionization reactions, with suppression or enhancement depending on spin conservation, aligning with a spin angular momentum coupling model.

Contribution

It introduces an all-optical method to prepare atomic spin states and demonstrates their effect on chemi-ionization reactions, revealing spin-dependent reaction dynamics.

Findings

Chemi-ionization is suppressed for non-spin-conserving collisions.

Chemi-ionization is enhanced for spin-conserving collisions.

Deviations suggest contribution of spin-violating channels.

Abstract

We demonstrate the control of $^4$He(2$^3$S$_1$)-$^7$Li(2$^2$S$_{1/2}$) chemi-ionization reactions by all-optical electron-spin-state preparation of both atomic species prior to the collision process. Our results demonstrate that chemi-ionization is strongly suppressed (enhanced) for non-spin-conserving (spin-conserving) collisions at thermal energies. These findings are in good agreement with a model based on spin angular momentum coupling of the prepared atomic states to the quasi-molecular states. Small deviations from the model indicate the contribution of the $^4\Sigma^+$ channel to the reaction rate which is in violation of spin conservation.