Ion neutralisation mass-spectrometry route to radium monofluoride (RaF)

TL;DR

This paper proposes a novel method to produce radium monofluoride (RaF) molecules using ion neutralisation mass spectrometry, leveraging their electronic structure for efficient neutralisation without dissociation.

Contribution

It introduces a new route for generating RaF molecules via charge exchange collisions of RaF+ ions with sodium atoms, based on their electronic structure properties.

Findings

Charge exchange collisions of RaF+ with sodium are nearly iso-enthalpic.

Large cross-sections are predicted for RaF neutralisation.

The method enables production of RaF molecules suitable for fundamental physics experiments.

Abstract

The diatomic molecule radium monofluoride (RaF) has recently been proposed as a versatile probe for physics beyond the current standard model. Herein, a route towards production of a RaF molecular beam via radium ions is proposed. It takes advantage of the special electronic structure expected for group 2 halides and group 2 hydrides: The electronic ground state of neutral RaF and its monocation differ in occupation of a non-bonding orbital of $\sigma$ symmetry. This implies similar equilibrium distances and harmonic vibrational wavenumbers in the two charge states and thus favourable Franck--Condon factors for neutralisation without dissociation in neutralising collisions. According to the calculated ionisation energy of RaF, charge exchange collisions of RaF$^+$ with sodium atoms are almost iso-enthalpic, resulting in large cross-sections for the production of neutral radium monofluoride.