Charge Exchange and Chemical Reactions with Trapped Th$^{3+}$

TL;DR

This study measures reaction rates of trapped Th$^{3+}$ ions with various gases, revealing that reactions with some gases occur at classical rates and involve charge exchange or chemical reactions, influenced by electronic states.

Contribution

It provides the first detailed analysis of Th$^{3+}$ reactions with different gases, highlighting charge exchange and chemical reaction pathways and their dependence on electronic configuration.

Findings

Reactions with CO₂, CH₄, and O₂ occur near Langevin rates.

Charge exchange dominates reactions with O₂ and CH₄.

Reaction rates with Ar, H₂, N₂ are significantly lower.

Abstract

We have measured the reaction rates of trapped, buffer gas cooled Th$^{3+}$ and various gases and have analyzed the reaction products using trapped ion mass spectrometry techniques. Ion trap lifetimes are usually limited by reactions with background molecules, and the high electron affinity of multiply charged ions such as Th$^{3+}$ make them more prone to loss. Our results show that reactions of Th$^{3+}$ with carbon dioxide, methane, and oxygen all occur near the classical Langevin rate, while reaction rates with argon, hydrogen, and nitrogen are orders of magnitude lower. Reactions of Th$^{3+}$ with oxygen and methane proceed primarily via charge exchange, while simultaneous charge exchange and chemical reaction occurs between Th$^{3+}$ and carbon dioxide. Loss rates of Th$^{3+}$ in helium are consistent with reaction with impurities in the gas. Reaction rates of Th$^{3+}$ with nitrogen and argon depend on the internal electronic configuration of the Th$^{3+}$.